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Six new species of palaeonemerteans (Nemertea) from Hong Kong
Zoological Journal of the Linnean Society (1999), 125: 151–196. With 23 figures Article ID: zjls 1997.0147, available online at http://www.idealibrary.com on
Six new species of palaeonemerteans (Nemertea) from Hong Kong RAY GIBSON FLS∗ School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF PER SUNDBERG Department of Zoology, Go¨teborg University, Medicinaregatan 18, S-400 31 Go¨teborg, Sweden Received February 1997; accepted for publication September 1997
One new genus and six new species of palaeonemerteans are described and illustrated from Hong Kong and the New Territories; these are Hubrechtella sinimarinus sp. nov. and Parahubrechtia jillae gen. et sp. nov. in the Hubrechtidae, and Callinera bergendali sp. nov., Carinina sinensis sp. nov., Tubulanus hylbomi sp. nov. and Tubulanus longivasculus sp. nov. in the Tubulanidae. These bring the known number of palaeonemertean species from Hong Kong to 11; a key to these species, based primarily upon features distinguishable in the living animals, is provided. 1999 The Linnean Society of London
ADDITIONAL KEY WORDS:—Taxonomy – morphology – Callinera – Carinina – Hubrechtella – Parahubrechtia gen. nov. – Tubulanus. CONTENTS
Introduction . . . . . . . . . . Material and methods . . . . . . Abbreviations . . . . . . . . . Observations . . . . . . . . . Family Hubrechtidae . . . . . Genus Hubrechtella Bergendal, 1902 . Hubrechtella sinimarinus sp. nov. Genus Parahubrechtia gen. nov. . . Parahubrechtia jillae sp. nov. . Family Tubulanidae . . . . . Genus Callinera Bergendal, 1900 . . Callinera bergendali sp. nov. . . Genus Carinina Hubrecht, 1885 . . Carinina sinensis sp. nov. . . . Genus Tubulanus Renier, 1804 . .
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∗ Corresponding author: Email: [email protected] 0024–4082/99/020151+46 $30.00/0
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Tubulanus hylbomi sp. nov. . . . Tubulanus longivasculus sp. nov. . Key to the palaeonemerteans of Hong Kong Acknowledgements . . . . . . . . References . . . . . . . . . . .
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INTRODUCTION
Several new species of nemerteans have recently been described from Hong Kong (Gibson, 1990, 1997; Gibson & Sundberg, 1992); among these, five are included in the two anoplan orders Archi- or Palaeonemertea. The taxon Archinemertea was originally proposed by Iwata (1960) to contain three genera, Cephalotrichella, Cephalothrix and Procephalothrix, which were previously included with the Palaeonemertea in the family Cephalothricidae. However, Sundberg & Hylbom (1994), using cladistic analyses to assess the phylogeny of the archi- and palaeonemerteans, concluded that their separation could no longer be supported. Although the cephalothricid genera form a monophyletic group within the clade Palaeonemertea, the retention of the Archinemertea as a distinct order would make the Palaeonemertea paraphyletic and Sundberg & Hylbom (1994) accordingly rejected the name Archinemertea. Based upon their arguments, five species of palaeonemerteans have thus been recorded from Hong Kong; these are Carinesta tubulanoides Gibson, 1990, Cephalotrichella alba Gibson & Sundberg, 1992, Hubrechtella alba Gibson, 1997, Procephalothrix arenarius Gibson, 1990, and Procephalothrix orientalis Gibson, 1990. During a visit to Hong Kong in 1989, six further species of palaeonemerteans were discovered by PS. The principal anatomical features of these species were included in the phylogenetic analyses of Sundberg & Hylbom (1994), under the reference numbers HK sp. 1 to HK sp. 6 inclusive, but in the present paper they are named and fully described for the first time.
MATERIAL AND METHODS
The nemerteans were collected during 1989 from sampling sites off the New Territories, Hong Kong (Fig. 1). Specimens were anaesthetized in either 7.5% MgCl2 or MS222, examined for external features and then fixed in seawater Bouin’s solution, sectioned at 7 lm in 58°C m.p. paraffin wax and stained by the Mallory trichrome method. Type material is deposited in the Stockholm Museum of Natural History (SMNH).
ABBREVIATIONS
BC BE BN CC CD
buccal nerve commissure buccal epithelium buccal nerve ciliated cerebral canal cephalic glands
CG CL CM CN CO
cerebral ganglia cephalic lacuna body wall circular muscle layer cephalic neural layer cerebral sensory organ
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CV DC DG DL DN DV EB EP EX FG FN FV GO IC IN LD LF
cerebral organ blood vessel dorsal cerebral commissure dorsal cerebral ganglion dorsolateral blood lacuna dorsal nerve mid-dorsal blood vessel epidermal basement layer epidermis excretory tubule foregut foregut nerve branch of foregut vascular plexus gonad body wall inner circular muscle layer intestine lower dorsal nerve longitudinal muscles between cerebral ganglia and epidermal basement layer
LM LN LO LP LV MS MT OC PI PN PR RB RC RD RM VB VC VG
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body wall longitudinal muscle layer lateral nerve cord lateral sensory organ longitudinal muscle plate lateral blood vessel posterior muscle sac of rhynchocoel mouth body wall outer circular muscle layer proboscis insertion proboscis nerve proboscis rhynchocoel body rhynchocoel rhynchodaeum proboscis retractor muscle blood vessel leading to rhynchocoel body ventral cerebral commissure ventral cerebral ganglion
OBSERVATIONS
Family Hubrechtidae Genus Hubrechtella Bergendal, 1902 Diagnosis. Gibson (1979a) defines the genus as palaeonemerteans with two body wall muscle layers consisting of outer circular and inner longitudinal fibres; brain and lateral nerve cords situated between epidermal ‘neural’ connective tissue layer (anteriorly) or epidermal basement membrane (posteriorly) and circular musculature of body wall; nervous system with a single pair of giant fibres extending through the brain lobes and lateral nerve cords; proboscis with two (outer longitudinal, inner circular) or three (outer and inner circular, middle longitudinal) muscle layers; rhynchocoel not fully body length; blood system with three main post-cerebral channels consisting of unpaired mid-dorsal and paired lateral vessels; no excretory system; no eyes; cerebral sensory organs well developed, positioned at rear of brain and enclosed by lateral blood vessels; sexes separate.
Hubrechtella sinimarinus sp. nov. (Figs 2–4) HK sp. 3 in Sundberg & Hylbom (1994) Type specimen. Holotype: immature female, series of transverse sections through the anterior and intestinal regions of the body (8 slides), SMNH 4889.
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Figure 1. Map of part of the New Territories, Hong Kong, to show the location of collecting sites referred to in the text. 1, Hoi Ha Wan; 2, Trawl 13; 3, Trawl 51; 4, Flat Island.
Type locality. Hoi Ha Wan (Location 1, Fig. 1), south-west of Flynn Point, from mussel beds on shell sand at 7 m depth. Etymology. The specific epithet, denoting that the species was found in the China Sea, is a composite between the Latin Sinae (an Oriental people mentioned by Ptolemy, now the Chinese) and marinus (of the sea). External features. The nemerteans were up to 15 mm long with slender bodies, 0.3 mm wide anteriorly, 0.5 mm posteriorly (Fig. 2). The spatulate head was clearly demarcated from the remainder of the body and had neither eyes nor cephalic furrows. The ventral mouth was visible about 1.5 mm behind the anterior tip. The general colour was an opaque white, although intestinal contents sometimes imparted a brownish tinge posteriorly.
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Figure 2. Hubrechtella sinimarinus sp. nov. A, drawing of complete specimen to show the general appearance of the body. B, enlargement to show the shape of the head. Scale bar applies to (A) only.
Body wall, musculature and parenchyma. As in other Hubrechtella species, the epidermis is better developed anteriorly. On the head it is up to 45 lm thick, decreasing posteriorly to a maximum of 30 lm or less in the intestinal regions. Unfortunately the epidermis has sloughed off from several parts of the body, so a detailed comparison between the distribution of the various gland cell types, described by Hylbom (1957) for the type species, Hubrechtella dubia Bergendal, 1902, cannot be made. Beneath the epidermis the basement membrane is distinct but thin, rarely more than 2–3 lm. In the head the nervous layer reported between the epidermal basement membrane and body wall circular muscle layer in some species (Hylbom, 1957; Gibson, 1979a, b), is also evident and can be traced back into the foregut region of the body, where it is 5–8 lm thick. The body wall muscle layers are typical for the genus. The circular layer is about 6–8 lm in maximum thickness throughout most of the body length, although tending to be less posteriorly, whereas the longitudinal muscles are 15–30 lm deep in the foregut region but up to 60 lm in the intestinal region. The so-called zigzag fibres reported in the longitudinal muscle layer of Hubrechtella dubia, Hubrechtella malabarensis Gibson, 1979, and Hubrechtella alba Gibson, 1997 (Hylbom, 1957; Gibson, 1979a; 1997), are also distinguishable in the present form (Fig. 3), although they are missing from other members of the genus (Kirsteuer, 1967; Gibson, 1979b). Parenchymatous connective tissues are nowhere strongly developed. Proboscis apparatus. The tip of the head, in front of the proboscis insertion, was unfortunately lost during sectioning; no observations can thus be made about the rhynchodaeum. The rhynchocoel is shorter than the body, extending about 65–70% of the body length; its wall contains separate circular and longitudinal muscle layers which are each mostly 4–6 lm thick, although in the foregut region the circular layer is better developed (Fig. 3). The proboscis insertion is presumed to be pre-cerebral, as in other members of the genus. In the retracted position the proboscis is about 165 lm in overall diameter and consists of an outer and richly glandular epithelium, up to about 60 lm thick, an outer circular muscle layer at most only two or three fibres thick, an inner
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Figure 3. Hubrechtella sinimarinus sp. nov. Camera lucida drawing of transverse section through the foregut region to show the organisation of various body structures. Note the zigzag arrangement of the muscle fibres in the proximal regions of the body wall longitudinal musculature.
longitudinal muscle coat 10–15 lm across and a thin but distinct inner lining (Fig. 4). The proboscis morphology is similar throughout the length of the organ. No proboscis nerves could be distinguished. The proboscis retractor muscle is well developed (Fig. 3). Alimentary canal. The slit-like mouth opens close behind the brain. The buccal wall, 60–70 lm or more thick, is richly glandular and densely ciliated. Two major types of gland cells are distinguishable, both containing coarsely granular secretions. Basophilic glands occur on all margins of the foregut, but the acidophils are mainly restricted to the dorsal and lateral margins. A delicate layer of circular muscles, at most only a few fibres thick and not evident in all parts of the foregut, surrounds the foregut, whilst a thin layer of longitudinal muscles dorsally extends between the foregut and rhynchocoel walls (Fig. 3); in several places isolated longitudinal muscle fibres can also be seen alongside and ventrolaterally to the foregut wall. The intestinal wall is up to 60 lm or more thick and contains only acidophilic glands. There are no lateral diverticula. Blood system. The arrangement of the cephalic blood supply is not known. In the cerebral ring a pair of rather compressed lateral lacunae extend back, one on either side of the rhynchocoel. These begin to enlarge as the dorsal and ventral brain lobes separate posteriorly and, anterior to the mouth, are penetrated by the cerebral sensory organs (Fig. 4). Unlike the condition in Hubrechtella alba (Gibson, 1997) the two vessels do not fuse ventrally behind the ventral cerebral commissure. A middorsal vessel extends below the rhynchocoel (Fig. 3) but no evidence of a rhynchocoelic villus, as found in some hubrechtids, could be distinguished. This condition is similar
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Figure 4. Hubrechtella sinimarinus sp. nov. Camera lucida drawing of oblique section through the cerebral region to show a ciliated cerebral canal, cerebral sensory organ, the anterior portion of the proboscis and the general arrangement of this part of the body.
to that described for Hubrechtella indica Kirsteuer (1967) and Hubrechtella queenslandica (Gibson, 1979b), which also have no rhynchocoelic villus. In the foregut region the two vessels do not form a vascular plexus, remaining separate throughout the length of the body in a lateral or ventrolateral position (Fig. 3). Several members of the genus are known to possess a foregut vascular plexus, formed by subdivision of the two lacunae, but none is found in Hubrechtella indica or Hubrechtella sarodravayensis (Kirsteuer, 1967). There is no evidence of pseudometameric transverse connectives between the blood channels in the intestinal region and none have been recorded for any other member of the genus. Nervous system. The brain lobes and lateral nerve cords are situated between the epidermal basement membrane and the body wall circular muscle layer. The brain lobes are well developed, the dorsal rather larger than the ventral. The slender dorsal cerebral commissure, 4–5 lm thick, is located posterior to the ventral commissure, which is 20–25 lm wide. Hubrechtella alba from Hong Kong, unlike the present form, is the only member of the genus known to possess two dorsal commissures (Gibson, 1997). The lateral nerves lead from the rear of the ventral ganglia; the giant nerve fibre, described in the lateral nerves for several Hubrechtella species, could not be distinguished in the present form. The fibrous core of each dorsal brain lobe is forked posteriorly into outer dorsal and inner ventral branches, the latter innervating the cerebral sensory organs (Fig. 4). This condition closely resembles that described for other members of the genus. Both upper and lower median dorsal nerves can be followed from the rear of the
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dorsal commissure back into the foregut region. The upper nerve runs between the epidermal basement layer and the body wall circular muscles, the lower in the longitudinal muscle layer. From the rear of the ventral commissure a single median nerve leads back towards the mouth; this nerve, evidently leading to the foregut neural supply, forks a short distance in front of the mouth but could not be traced further (Fig. 4). Sense organs. As in other species of Hubrechtella, there are neither eyes nor lateral sensory organs. The cerebral sensory organs are large and well developed (Fig. 4). Towards the rear of the brain the lateral epidermis forms a short, shallow indentation lined by long (15 lm) cilia and entirely lacking gland cells. At the rear of the indentation on each side of the body a ciliated cerebral canal, 20 lm in diameter, leads directly inwards in a medioventral direction to a cerebral organ (Fig. 4). The cerebral canals enter the blood vessels in the brain region, enter the cerebral organs which are composed of a complex of glandular and neuroganglionic cells below the cerebral organ nerve, and then extend towards the rear of the organs close to their outer lateral surface. The cerebral organs are contained entirely within the lumen of each lateral blood lacuna except where their ciliated canals enter them anteriorly. Each organ is ovoid, about 50–55 lm wide, 90 lm in dorsoventral extent and 110 lm long; the organs reach back to the oral region. Excretory system. As in other species of Hubrechtella (Hylbom, 1957; Kirsteuer, 1967; Gibson, 1979a, b, 1997), no evidence of an excretory system has been found. Reproductive system. The single specimen is an immature female. The ovaries are packed close together in the intestinal region, forming ‘blocks’ of reproductive organs extending along the lateral and dorsolateral margins of the body. Systematic discussion. Nine species of Hubrechtella have been described previously (Gibson, 1995, 1997), all sharing many anatomical features. Sundberg & Hylbom’s (1994) phylogeny of the palaeonemerteans shows that the present form belongs in a clade along with four of these, including the type species for the genus Hubrechtella dubia. The arrangement of the body wall layers, well developed cerebral sensory organs intimately associated with the blood system, position of the central nervous system in relation to the body wall and absence of an excretory system, enable the present taxon to be placed in the genus. Among the previously known hubrechtellids two species have been recorded from Madagascar (Kirsteuer, 1967), two from Australia (Gibson, 1979a, b) and one (Hubrechtella alba) from Hong Kong (Gibson, 1997); the remaining four are known only from European waters (Gibson, 1995). Hubrechtella alba differs from the present form in its relatively much smaller-sized proboscis, possession of two dorsal cerebral commissures, organization of its anterior blood supply into a foregut vascular plexus, and in having a mid-dorsal blood vessel within a rhynchocoelic villus (Gibson, 1997). The Indo-Pacific forms differ from the present species in the following ways: Hubrechtella queenslandica possesses a proboscis with three muscle layers and no zigzag fibres in its body wall longitudinal musculature (Gibson, 1979b), and the three other taxa (H. indica, H. malabarensis and H. sarodravayensis) do not possess a circular muscle layer around their foreguts (Kirsteuer, 1967; Gibson, 1979a), and H. sarodravayensis and H. indica have no zigzag fibres in their longitudinal muscle layers. The present form cannot therefore be identified as belonging to any of the previously known
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species of Hubrechtella and it is accordingly described as a new species, for which the name Hubrechtella sinimarinus is proposed.
Genus Parahubrechtia gen. nov. Diagnosis. The genus Parahubrechtia gen. nov. may be defined as palaeonemerteans that lack head furrows; body wall musculature comprising outer and inner circular and middle longitudinal layers; muscle crosses between body wall circular layers missing; without cerebral sensory organs; lateral organs present; cephalic region with nerve layer; proboscis with outer circular and inner longitudinal muscle layers; proboscis nerves present; brain and lateral nerve cords situated between epidermal basement membrane and body wall outer circular muscles; nervous system with neither neurochords nor neurochord cells; buccal nerves paired; intestine without lateral diverticula; rhynchocoel wall primarily with circular musculature but isolated longitudinal fibres also present; excretory system simple, anteriorly penetrating lateral blood vessels; blood vascular system simple, without mid-dorsal vessel; eyes absent; sexes probably separate; with neither frontal glands nor apical organ. Etymology. The generic name, indicating its affiliation with the family Hubrechtidae, is formed from the Greek prefix para (near or alongside) and the name of the type genus for the family, Hubrechtia. Type species. Parahubrechtia jillae sp. nov.
Parahubrechtia jillae sp. nov. (Figs 5–8) HK sp. 2 in Sundberg & Hylbom (1994) Type specimens. Holotype: female, complete set of transverse sections (4 slides), paratype: female, complete set of transverse sections (4 slides), SMNH 4890. Type locality. Hoi Ha Wan (Location 1, Fig. 1), southwest of Flynn Point, collected from 7 m depth on shell sand. Etymology. The species is named after Jill Gibson, the first author’s wife, who has unfailingly supported his research interest in nemerteans. External features. The nemerteans were 6–10 mm long but only about 0.3 mm wide. The body was rather flattened dorsoventrally, the spatulate head distinct in life (Fig.
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Figure 5. Parahubrechtia jillae gen. et sp. nov. Drawing to show the general appearance of a living specimen.
Figure 6. Parahubrechtia jillae gen. et sp. nov. Camera lucida drawing of transverse section through the cephalic region.
5). The intestine was clearly visible through the whitish, translucent, posterior half of the body, the pointed posterior tip looking distinctly fragile. The body exhibited a distinct thickening and the epidermis was milky white and papillose, about onethird back from the anterior end. Body wall, musculature and parenchyma. The epidermis in the cephalic region is 30–40 lm tall, internally lined by a thin but distinct connective tissue membrane (Fig. 6).
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Figure 7. Parahubrechtia jillae gen. et sp. nov. Camera lucida drawing of transverse section through the anterior intestinal region close to the lateral sensory organs.
Behind the brain the epidermal height is reduced to about 20–30 lm, a further reduction occurring throughout the intestinal region where the epidermis is often only 15 lm or less thick. Gland cells of various types are distributed throughout the length of the body, but close in front of the brain a zone of loosely distributed Orange G positive glands, containing coarsely granular cytoplasm, forms a distinct layer in the distal third of the epidermis. In the intestinal region, just in front of the nephridiopores and lateral sensory organs, a band of densely packed and strongly acidophilic glands, filling the proximal half of the epidermis, encircles the body. This region extends back for 100–120 lm before suddenly disappearing; similar glands are not found elsewhere in the epidermis. The body wall musculature comprises outer circular, middle longitudinal and inner circular layers which, in the foregut region, are respectively some 3–6 lm, 15–25 lm and 2–3 lm thick. In the brain region the outer circular muscles are reduced in thickness, but the longitudinal layer is up to 35–40 lm deep. Precerebrally isolated dorsoventral muscle fibres cross the head between the various cephalic structures. The inner circular layer is missing from the cephalic and cerebral regions but extends for a short distance into the intestinal part of the body (Fig. 7). Between the rhynchocoel and foregut wall a loosely arranged layer of longitudinal muscles, mostly only a single fibre thick, extends back into the intestinal region (Fig. 7) almost as far as the posterior end of the rhynchocoel. There are no intrinsic muscles associated with any part of the gut, and dorsoventral muscle bundles are absent from the intestinal region. The outer circular and longitudinal muscle layers are not as well developed in the posterior half of the body. Parenchymatous connective tissues are poorly developed.
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Figure 8. Parahubrechtia jillae gen. et sp. nov. Camera lucida drawing of transverse section through the brain region just behind the ventral cerebral commissure.
Proboscis apparatus. The proboscis pore is subterminal and ventral; it opens about 60–70 lm behind the tip of the head. It leads into a rhynchodaeum whose epithelium, 5–15 lm thick, is neither ciliated nor glandular (Fig. 6). The proboscis insertion is situated between the brain lobes. The two proboscis nerve roots, which emerge from the dorsal margins of the ventral ganglionic lobes, enter the proboscis insertion ventrolaterally. The rhynchocoel, about half the body width in diameter, extends for about 60% of the body length. Its wall is composed principally of a circular muscle layer, 5–6 lm thick, but isolated longitudinal muscle fibres, which do not form a definite layer, extend between the circular muscles and the innermost body wall musculature (Fig. 7). The proboscis (Figs 6–8) is slender, about 70–80 lm in diameter when retracted. It has a more or less uniform construction throughout its length, comprising a glandular epithelium 12–20 lm tall, an outer circular muscle layer 2–3 lm across, an inner longitudinal muscle coat 3–6 lm thick, and a thin inner lining. The two proboscis nerves are situated on opposite sides of the organ between the epithelium and circular muscle layer (Fig. 8); each nerve is 6–8 lm in diameter. Below each nerve, but separated from it by the circular muscles, a ‘strand’ of Orange G positive tissue extends the full proboscis length; the significance of these tissues is not known. The thick retractor muscle is attached to the dorsal rhynchocoel wall near its posterior end. Alimentary canal. The ventral mouth is situated immediately behind the brain. The buccal epithelium is 10–20 lm thick, glandular and ciliated. Throughout the foregut the epithelium is little folded and thinner than that of the buccal region. The intestinal epithelium, up to 30 lm thick, has a typical palaeonemertean appearance. There are no lateral diverticula, both the intestine (Fig. 7) and foregut
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essentially forming a simple tubular canal arching below the rhynchocoel. Behind the rhynchocoel the intestine occupies most of the body space between the lateral rows of gonads. Blood system. The simple blood system (Figs 6–8) is similar to that described for cephalothricid palaeonemerteans. It consists of a single pair of thin-walled, spacious lateral vessels, joined anteriorly by a cephalic loop in front of the proboscis pore and posteriorly by a transverse supra-intestinal connective. There is no mid-dorsal vessel and no other transverse connectives. In the foregut and anterior intestinal regions the lateral vessels run internal to the body wall inner circular muscles, but close in front of the lateral sensory organs the vessels pass through this layer and continue posteriorly between it and the body wall longitudinal musculature (Fig. 7). Behind the posterior limit of the inner circular muscles the vessels continue just internal to the longitudinal layer. Nervous system. The brain, situated between the epidermal basement layer and body wall outer circular musculature, is comparatively large and well developed. The dorsal lobes are larger than, and extend in front of, the ventral. Longitudinal muscle bundles between the brain and epidermis, as described later for the two Tubulanus species, are missing. The dorsal lobes are more lateral in position than the ventral lobes (Fig. 8). Dorsal and ventral cerebral commissures are at about the same level, the former 12–15 lm thick, the latter 20–22 lm. Neither an inner nor outer neurilemma can be distinguished, nor are there any neurochord cells. The longitudinal nerves lead from the rear of the ventral ganglia and extend the full length of the body in a lateral position (Fig. 7). The peripheral nervous system is also well developed. In the head a distinct neural layer, up to 8–10 lm thick, is present between the epidermal basement layer and the body wall outer circular musculature (Fig. 6). Several distinct nerve tracts are evident in the layer, which originates from the anterior margins of both dorsal and ventral ganglionic lobes. A median dorsal nerve, 12 lm thick, extends backwards immediately below the epidermal basement layer; a lower dorsal nerve, situated internal to the outer circular musculature (Fig. 7), is distinguishable only in the anterior intestinal region. The proboscis nerves lead from the dorsal surface of the ventral brain lobes, and close behind these a single nerve emerges from the inner ventrolateral border of each ventral lobe, curving upwards and inwards to a thick (20 lm or more) transverse commissure located close in front of the mouth just below the rhynchocoel (Fig. 8). The two buccal nerves, 15 lm in diameter, lead from the rear of this commissure, lead back on either side of the mouth and can be followed for only a short distance adjacent to the foregut wall. Sensory organs. The present species possesses neither eyes nor cerebral sensory organs. What are interpreted as simple lateral epidermal sensory organs are present, however, just in front of the nephridiopores. Level with the dorsal margins of the lateral nerves a simple pit on each side of the body (Fig. 7) leads to an intraepidermal chamber, some 15 lm in diameter, which ends close to the lateral nerves. The epidermal tissues adjacent to these pits, which are lined by long dense cilia, lack the gland cells which occur elsewhere at this level. Frontal glands and apical organ. Neither an apical organ nor frontal glands are present in this species.
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Figure 9. Callinera bergendali sp. nov. Drawing to show the general appearance of a living specimen.
Excretory system. The excretory system, extending for approximately 150 lm, opens just behind the dense band of acidophilic epidermal gland cells. A single large collecting tubule on each side lies immediately above each lateral blood vessel, outside the body wall inner circular muscle layer (Fig. 7). The tubules are thickwalled (10–12 lm) for most of their length, but are anteriorly thinner-walled where they lie adjacent to the outer lateral margins of the vessels and bulge into each vessel lumen. Small amounts of Orange G positive material are associated with the intravascular inpushings, but whether these represent glandular terminal organs, as described for some palaeonemertean species, could not be determined. Posteriorly the collecting tubules end in slender efferent ducts which open via a single dorsolateral nephridiopore on each side of the body. Reproductive system. The sexes, as in other hubrechtid species, are probably separate. Both specimens obtained are female, the ovaries lying in a densely distributed lateral row on either side of the body, commencing just before the end of the rhynchocoel. Ova in several stages of development are distinguishable within each individual, larger eggs containing a single ovoid nucleus about 40 lm in diameter in which a single distinct nucleolus, 7–8 lm across, is positioned excentrically. Systematic discussion. This species makes a clade in Sundberg & Hylbom (1994: Fig. 9) with Hubrechtella dubia, H. malabarensis, H. queenslandica, H. sarodravayensis, Tetramys ramicerebrum Iwata, 1957, Tubulanus lucidus Iwata, 1957, and HK sp. 3, thus supporting Hylbom’s (1957) suggestion that Tubulanus lucidus should also be included in the genus Hubrechtella. According to the traditional classification of nemertean families and genera, both Hubrechtella and Tetramys belong in the Hubrechtidae, which also includes two other genera, Coeia and Hubrechtia. Sundberg & Hylbom’s (1994: Table 4) matrix of characters used to define the various palaeonemertean genera shows that Hubrechtella and Tetramys share several anatomical features, including length at the onset of sexual maturity, absence of eyes, presence of a neural layer rather than separate cephalic nerves, position of the cerebral ganglia and lateral nerve cords, presence of paired buccal nerves, and occurrence of a single mid-dorsal blood vessel that enters the rhynchocoel wall. Most Hubrechtella species also resemble Tetramys in lacking a horizontal muscle plate between the rhynchocoel and alimentary canal and in lacking lateral sensory organs. Hubrechtella queenslandica resembles Tetramys in possessing three proboscis muscle layers, whereas all other Hubrechtella species known have only two. The present taxon differs from both these genera in lacking a mid-dorsal blood vessel but possessing a horizontal muscle plate between the rhynchocoel and foregut,
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and in being much smaller at the onset of sexual maturation. It also differs from Tetramys in possessing two, rather than three, proboscis muscle layers. Hubrechtia, the type genus for the family Hubrechtidae, differs from the Hong Kong form in possessing cerebral sensory organs, which are also found in Hubrechtella and Tetramys, and in having two nerves in its rhynchodaeal epithelium, a median dorsal blood vessel and intestinal diverticula, whilst Coeia has cerebral but no lateral sensory organs, no proboscis nerves, intestinal diverticula, a mid-dorsal blood vessel and a rhynchocoel wall with an inner longitudinal muscle layer. It is accordingly concluded that the present form, whilst being closely related to these hubrechtid genera according to the analyses of Sundberg & Hylbom (1994), is sufficiently different to warrant separate generic status and it is therefore named Parahubrechtia jillae gen. et sp. nov. Family Tubulanidae Genus Callinera Bergendal, 1900 Diagnosis. Hylbom (1957: 552) gave the following diagnosis for the genus Callinera: “Nervous system situated between the basement membrane and the outer circular muscle layer. No cerebral sense organs. In the posterior end of the proboscis sheath a peculiar, well-developed muscle sac. Basement membrane thin.” Callinera bergendali sp. nov. (Figs 9–12) Callinera sp. in Sundberg et al. (1992), HK sp. 4 in Sundberg & Hylbom (1994) Type specimens. Holotype: immature, complete set of transverse sections (5 slides), paratypes: four sets of 4 slides each, transverse sections of immature specimens, SMNH 4891. Type locality. Hoi Ha Wan (Location 1, Fig. 1), north of Joss House Point, 7 m depth in heterogeneous shell sand. Other locations. Hoi Ha Wan, Station B6, lower shore intertidal, coarse sand with H2S near the surface (see Sundberg et al., 1992). Etymology. The species is named in honour of the Swedish zoologist, Professor David Bergendal, who studied Scandinavian nemerteans around the turn of the present century and established the genus Callinera. External features. The specimens found were up to 8 mm long and 0.3 mm wide. The body tapered at both ends (Fig. 9). They were whitish, somewhat opaque, with the anterior half of the body more transparent than the milky posterior region. Eyes, cephalic furrows and mouth were indistinguishable in life. Body wall, musculature and parenchyma. The cephalic epidermis is 30–45 lm tall; in its most anterior regions there is no obvious basement membrane, this beginning to appear commensurate with the anterior limits of the cephalic nerves and is then distinct throughout the remaining length of the body. In the cephalic region two
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principal types of epidermal secretory cells are distinguishable; dorsally the glands are large, somewhat vacuolate, irregular in shape and have no particular staining affinities, whereas ventrally the glands are smaller, basophilic and contain a coarsely granular cytoplasm. In the brain region the epidermis laterally is often only about 10 lm thick and contains few secretory cells, but dorsally and ventrally has a similar height to the more anterior portions of the head. Vacuolate glands are both more abundant in the oral region and extend to most sides of the body. A short distance behind the mouth the glandular components of the epidermis change abruptly. Vacuolate cells almost disappear, to be replaced by strongly acidophilic rhabditoid glands and the granular basophils. These two glandular types together occupy the proximal half of the epidermis. This epidermal region extends posteriorly for some 350 lm before ending as abruptly as it started. For the remaining length of the body the basophilic glands are the most abundant, interspersed with occasional vacuolate cells. In the posterior body regions the epidermis is reduced to a height of 20 lm or less. The epidermal basement membrane is 2–3 lm thick in the oral and foregut regions, but only 1–1.5 lm further back. Connective tissue fibrillae lead from the distal surface of the basement layer into the proximal portions of the epidermis, but there is no inner meshwork layer as, for example, in some Tubulanus species. The body wall musculature comprises outer circular, middle longitudinal and inner circular layers, respectively some 3 lm, 30 lm and 1–2 lm thick in the foregut region of the body (Fig. 10). The inner circular layer does not extend into the head, anteriorly ending in the cerebral region, whereas posteriorly it reaches to the hind end of the body although it is often reduced to a single fibre’s thickness and is difficult to distinguish. There are no muscle crosses between the two circular muscle layers, and no dorsoventral muscles in the intestinal region. Commencing just behind the mouth an extremely thin longitudinal muscle plate extends between the rhynchocoel and gut wall; this continues into the intestinal region but terminates in front of the rhynchocoel muscular sac. Cellular parenchyma is not extensive but is evident in the dorsolateral parts of the foregut region (Fig. 10). Proboscis apparatus. The proboscis pore is subterminal. It leads into a tubular rhynchodaeum some 45 lm in overall diameter, whose unciliated epithelium is arranged into four longitudinal blocks of tissue, each about 15–20 lm in maximum width. This condition closely resembles that described for Callinera buergeri Bergendal, 1900. The rhynchodaeum is enclosed by a thin but distinct connective tissue layer, from which fibrils emerge irregularly to lead dorsally or ventrally between the longitudinal muscle fibres. Behind the brain the quadrate arrangement of the rhynchodaeal epithelium tends to become less obvious and the epithelium contains large and irregularly-shaped gland cells, with finely fibrillar cytoplasm, which appear the same as the lightly basophilic cephalic glands of other nemerteans. Towards its posterior end, immediately in front of the proboscis insertion, the rhynchodaeum narrows to form a short tubular region, 15–18 lm in diameter, that is enclosed by a loosely disposed layer of circular muscle fibres. The proboscis insertion is behind the brain, above where the mouth opens into the foregut. The rhynchocoel is approximately 20–25% of the body length and posteriorly ends in a well developed muscle sac (Fig. 11). For most of its length the rhynchocoel forms a spacious but thin-walled chamber, between 40–60% of the body width and
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Figure 10. Callinera bergendali sp. nov. Camera lucida drawing of transverse section through the posterior foregut region to show the arrangement of the various body structures.
lined by a delicate layer of circular muscles, about 2 lm in maximum thickness, and a thin lining epithelium. Towards its posterior end, however, it narrows sharply to form a dorsal tubular canal, only about 40 lm in diameter (i.e. < 10% of the body width) lined by an epithelium that is up to 15 lm thick ventrally. This slender canal ends in a muscular sac formed on the ventral wall of the rhynchocoel; the lumen of the rhynchocoel in this region appears as a narrow and dorsoventrally compressed tube. A posterior rhynchocoel muscle sac or bulb is found in all the Callinera species known, but is not recorded from any other palaeonemertean taxon. The proboscis is extremely slender, at most 60–65 lm in diameter when retracted. It nevertheless possesses a complex construction, with several histologically distinct regions recognisable. The most anterior portion, extending back from the proboscis insertion, is about 500 lm long and consists of a thin outer epithelium with no evident gland cells, an outer longitudinal musculature organised into four distinct blocks of fibres, an extremely thin connective tissue layer and a flattened inner lining. Two small proboscis nerves are evident on opposite sides of the organ between the outer epithelium and the longitudinal musculature. Towards the rear of this region the arrangement of the longitudinal musculature into four blocks becomes less distinct and, just before this region merges into the second part of the proboscis, the longitudinal muscle fibres form a single complete layer. In the second region
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Figure 11. Callinera bergendali sp. nov. Camera lucida drawing of transverse section through the posterior muscle sac of the rhynchocoel.
the epithelium, 8–10 lm thick, is arranged so that opposing sides form a wide Vshape appearing like a double chevron in transverse sections (Fig. 10). One side of this ‘chevron’ contains many Orange G positive glands, but the other has a mostly striated appearance with few glands. The longitudinal musculature of this region is restricted mainly to that side of the proboscis with a glandular epithelium. No nerves could be distinguished in this, or any subsequent, parts of the proboscis. In the third region the epithelium is asymmetrically developed; on one side it is 15–20 lm thick and dominated by large, lightly basophilic gland cells with finely particulate cytoplasm, on the other side the epithelium is almost indistinguishable. The fourth and most posterior portion of the proboscis, terminating in the longitudinal retractor muscle, contains an outer epithelium in which coarsely granular Orange G positive glands predominate and the remaining layers of the organ are almost non-existant. The proboscis retractor muscle leads to the dorsal rhynchocoel wall in front of the posterior muscle sac. Alimentary canal. The small, slit-like mouth opens either below the rear of the brain or immediately behind it, depending upon the degree of contraction of the individual. The foregut epithelium is up to 15 lm or more thick, densely ciliated and glandular, although not as deeply folded as in other members of the genus (Fig. 10).
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Figure 12. Callinera bergendali sp. nov. Camera lucida drawing of transverse section through the mid-cerebral region to show dorsal and ventral cerebral commissures.
The junction between foregut and intestine is marked by a change in the nature of the gland cells. The intestinal epithelium, up to 30 lm or more thick, histologically resembles that described for other species of Callinera. There are no lateral diverticula or pouches, the intestine essentially forming a simple tubular canal. The general organisation of the gut in the Hong Kong species shows no major differences from that described for the Scandinavian or British taxa. Blood system. The blood system in the present species is much more simple than in other species of Callinera. In the head, a pair of spacious thin-walled lateral cephalic lacunae meet in front of the proboscis pore by a wide transverse connective. The two cephalic lacunae continue posteriorly through the cerebral ring (Fig. 12), with almost no reduction in size, for most of the foregut region extending internal to the body wall inner circular muscle layer on either side of the rhynchodaeum and dorsolateral to the alimentary tract but moving outside the muscle layer (Fig. 10) just before the excretory system commences. In the intestinal portion of the body the lacunae develop thicker walls and gradually become smaller as they approach the rear of the rhynchocoel (Fig. 11). Behind the muscular bulb of the rhynchocoel, as the intestine expands to occupy more of the available body space, the two lateral vessels become very compressed, to the extent that in many parts of the intestinal region they are virtually indiscernible. There is no evidence of pseudometameric transverse connectives linking the lateral vessels in the intestinal region, nor is there any trace of a mid-dorsal blood vessel. Nervous system. The brain and lateral nerve cords are situated between the epidermal basement membrane and outer circular body wall muscle layers. The cerebral ganglia are well developed and transversely linked by a single dorsal and ventral commissure, respectively 8–10 lm and 20–22 lm thick (Fig. 12). In one specimen
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dorsal and ventral commissures are situated at the same level, in the other the dorsal is anterior to the ventral. A delicate inner neurilemma is distinguishable, but there is no outer neurilemma. Neither neurochords nor neurochord cells are present. The longitudinal nerves extend back from the rear of the ventral cerebral ganglia in a lateral position (Figs 10, 11). From the rear of each ventral cerebral lobe, close behind the ventral commissure, a distinct nerve leads back for a short distance and then turns dorsally to fuse with its partner, forming a ventral ganglionic mass below the rhynchodaeum. Almost immediately, this neural mass divides to form a pair of large (20 lm diameter) buccal nerves which continue posteriorly past the mouth, moving to a more ventrolateral position as they do so. Behind the mouth the nerves can only be traced in the parenchyma below the ventrolateral foregut margins for a short distance; their ultimate fate was not determined. From the rear of the dorsal commissure the single median dorsal nerve, which emerges to extend posteriorly through the foregut region (Fig. 10), divides into two (Fig. 11) close in front of the rhynchocoel muscle sac; the posterior limits of these nerves were not traced. Several distinct nerves run anteriorly from the front of the brain. They form a more or less continuous ‘layer’ immediately below the epidermal basement membrane, although individual nerves remain clearly distinguishable. Farther forwards the nerves become smaller and less obvious and are eventually impossible to find. Sensory organs. As in other species of Callinera, the present form possesses neither eyes nor cerebral sensory organs. A pair of lateral epidermal sensory organs is situated at the same level of the body as the nephridiopores. The organs appear as elongate lateral furrows, about 100 lm long, extending about 30 lm into the epidermis just above the lateral nerves. The epidermal tissues immediately adjacent to these furrows have a distinctly striated appearance but are not otherwise separated from them. Frontal glands and apical organ. Neither an apical organ nor frontal glands can be distinguished in the present species. Excretory system. The excretory system is well developed and extends for approximately 440 lm from the foregut into the anterior intestinal region. A single thick-walled (8–10 lm) ciliated collecting tubule extends dorsolaterally in the parenchyma on either side of the body, close above the lateral blood vessels (Fig. 10). In their anterior regions the tubules penetrate the blood vessels and are associated with gland-like masses hanging in each blood vessel lumen. The collecting tubules narrow posteriorly before turning dorsolaterally into the slender (6–7 lm overall diameter) efferent canals which lead through the body wall layers to small nephridiopores, located just behind where the foregut leads into the intestine and close in front of the rhynchocoel muscle sac. Reproductive system. All the specimens collected were sexually immature. Systematic discussion. The Hong Kong species, together with Callinera buergeri and C. monensis Rogers, Gibson & Thorpe, 1992, form a distinct and well-supported clade in Sundberg & Hylbom (1994); C. buergeri forma grandis Bergendal, 1903, was identified by Rogers et al. (1992) as a distinct species and listed as C. grandis Bergendal, 1903, by Gibson (1995). Sundberg & Hylbom (1994) chose not to recognize the
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specific status of this form but had it been included in their analyses it too would have belonged in the same clade. One of the major characters identifying this clade as a monophyletic group is the powerfully developed rhynchocoel muscle sac, formed from the posterior circular muscle layer. Rogers et al. (1992) tabulated the major anatomical characters that could be used to distinguish between the three species of Callinera then known. The present species differs from C. grandis and C. monensis in possessing lateral sensory organs near the nephridiopores, from C. buergeri and C. grandis in possessing only a single dorsal cerebral commissure, and from C. grandis in lacking subepidermal glands, in its cephalic blood supply consisting of two spacious lacunae and in its foregut nerves fusing just in front of the mouth to form a short single median ventral nerve. The blood supply in the head of the present species also differs from that of C. buergeri and C. monensis, in both of which there is essentially a single thin-walled lacuna irregularly subdivided into four longitudinal channels. These differences justify the Hong Kong form being identified as a new species, Callinera bergendali. Genus Carinina Hubrecht, 1885 Diagnosis. Hylbom (1957: 541) gave the following diagnosis for the genus Carinina: “Brain and lateral nerves situated in the epidermis; epidermis very high; basement membrane thin; body musculature consisting of outer circular, longitudinal and inner circular muscle layer; a thin longitudinal muscle plate present between the proboscis sheath and the gut; muscular wall of the proboscis sheath with circular muscle layer only; excretory organs with gland-like anterior parts in close connection with the lateral blood vessels, nephridial canals running backwards from the glandlike portions inside the inner circular muscle layer, in their posterior part turning at right angles towards the body surface where they open in an excretory pore; two proboscis nerves running forwards from the ventral commissure of the brain entering the rhynchodaeum in the tip of the head.” In his key to the tubulanid genera Hylbom separates Carinina from Callinera and Tubulanus by the position of the brain and lateral nerve cords in the epidermis, rather than between the epidermal basement layer and body wall outer circular muscle layer. Carinina sinensis sp. nov. (Figs 13–15) HK sp. 1 in Sundberg & Hylbom (1994) Type specimen. Holotype: immature female, series of transverse sections from the anterior tip back into the posterior intestinal region (5 slides), SMNH 4892. Type locality. Hoi Ha Wan (Location 1, Fig. 1), south-west of Flynn Point, 7 m depth in shell sand. Etymology. The specific epithet is the New Latin word sinensis (= of China) and indicates the geographical region from where the species was obtained. External features. The single specimen obtained was about 7–8 mm long, with a transparent body through which the intestine was clearly visible posteriorly. The
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Figure 13. Carinina sinensis sp. nov. Camera lucida drawing of transverse section through the cephalic region.
appearance of the specimen in life was virtually identical to that described for Parahubrechtia jillae gen. et sp. nov., with which it was found, and the two taxa could only be distinguished after histological examination. Body wall, musculature and parenchyma. The cephalic epidermis (Fig. 13) is 60–66 lm tall dorsally and ventrally, mostly rather less on the lateral margins. Throughout much of the head distinct radial fibres extend in the proximal half of the epidermis between the cephalic nerves; these fibres appear to radiate from the outer circular muscle layer. Anteriorly no gland cells are distinguishable, but towards the front of the brain isolated acidophilic glands begin to appear within the middle to proximal levels of the epidermis. In the brain region (Fig. 14) the non-neural parts of the epidermis are reduced to a height of only 15–25 lm, and the acidophilic glands begin to increase their density. Other isolated refractile glands, located distally, are also evident in the epidermis of the brain region. Behind the brain, epidermal height again increases to 25–50 lm (Fig. 15) and the acidophilic glands are densely packed and form a distinct proximal layer extending for almost 1 mm post-cerebrally before they abruptly disappear. Throughout the intestinal region the epidermis is gradually reduced posteriorly to a maximum height of some 20–25 lm. The epidermal basement layer throughout the body is thin. The body wall musculature comprises outer circular and inner longitudinal layers, respectively 4–5 lm and 15–30 lm thick in the foregut region of the body. An inner circular layer, 4–5 lm thick, is present throughout most of the foregut region (Fig.
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Figure 14. Carinina sinensis sp. nov. Camera lucida drawing of transverse section through the posterior cerebral region to show the mouth, cerebral sensory organs and arrangement of the blood system.
15), commencing just behind the mouth. The outer circular muscles are reduced to a thickness of 2–3 lm in the intestinal regions, but the longitudinal layer may be 60 lm or more wide and the inner circular musculature forms a delicate layer, one or two fibres thick, enclosing the intestine behind the end of the rhynchocoel. A layer of longitudinal muscle fibres, 2–4 lm deep, extends between the rhynchocoel and gut (Fig. 15) for most of the foregut length, but this layer ends anteriorly at the proboscis insertion, located behind the mouth, and in its place there is a transverse band of muscle fibres derived from both body wall circular muscle layers. The transverse band, up to 7–8 lm or more thick, effectively separates the body wall longitudinal muscle layer into dorsal and ventral portions above the mouth, where it passes under the rhynchodaeal wall. Longitudinal fibres are missing from the lateral body margins (Fig. 14). The inner circular layer disappears in front of the mouth, but the transverse muscle band continues forwards through the cerebral ring to contribute to a band of circular fibres enclosing the anterior portion of the rhynchodaeum (Fig. 13). Fibres radiate outwards from this rhynchodaeal muscle layer towards the lateral cephalic borders. No dorsoventral muscle bundles can be distinguished in the intestinal regions, and parenchymatous connective tissues are barely developed.
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Figure 15. Carinina sinensis sp. nov. Camera lucida drawing of transverse section through the foregut region.
Proboscis apparatus. The proboscis pore opens ventrally just behind the tip of the head. It leads into a rhynchodaeum (Fig. 13) whose ciliated epithelium for most of the cephalic length is 30–55 lm in height and contains isolated acidophilic and basophilic gland cells. Just behind the proboscis pore two of the nerves that comprise the cephalic neural layer turn inwards and enter the rhynchodaeal epithelium. These nerves can be traced the full length of the rhynchodaeum (Figs 13, 14), through the proboscis insertion and into the proboscis. The rhynchodaeum, with an overall diameter of some 120 lm, occupies much of the cephalic space but is somewhat reduced in diameter as it passes through the cerebral ring. Here its epithelium is also reduced to a maximum height of 12–15 lm. The rhynchodaeum is about 45 lm wide and 85 lm in dorsoventral height as it approaches the front of the mouth, gradually becoming smaller as it passes the oral region until, just in front of the proboscis insertion, it forms a narrow tubular canal about 30 lm in overall diameter, enclosed by a layer of circular muscle fibres. The proboscis insertion is situated post-orally. The rhynchocoel is approximately half the length of the body, its wall containing mainly circular fibres which form a layer 8–10 lm thick. The fibres of the rhynchocoel circular musculature cannot be distinguished from those of the body wall inner circular layer mid-dorsally, but on either side of this region isolated longitudinal muscle fibres run between the rhynchocoel and inner circular muscle layers. The proboscis (Fig. 15) contains two histologically distinct regions. In the retracted position, the anterior and longer portion is about 115 lm in overall diameter and contains a glandular epithelium up to about 15 lm thick, an outer circular muscle
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stratum no more than 3–4 lm across, an inner longitudinal muscle layer at most 15 lm deep, and a delicate inner lining. The two proboscis nerves are distinct and run in the proximal portion of the epithelium on either side of the proboscis (Fig. 15). Farther back, this portion of the proboscis is slightly larger, with an overall diameter of 125–130 lm, its epithelium is, in places, 25–30 lm or more thick, but its longitudinal muscle layer is progressively reduced to a maximum thickness of only 5–6 lm. In contrast, the posterior portion of the proboscis has an epithelium with a distinctly vacuolate appearance, no proboscis nerves can be distinguished, and both muscle layers are reduced to only one or two fibres thickness and are often difficult to see. Alimentary canal. The small mouth (Fig. 14) is situated below the rear portion of the brain. It opens into a foregut whose richly glandular and densely ciliated epithelium is, at first, up to some 30 lm thick, and moderately deeply folded (Fig. 15). Farther back, however, the foregut wall is unfolded and the epithelium reduced to a thickness of 15 lm or less; this posterior half of the foregut forms a dorsoventrally compressed canal arching below the ventral half of the rhynchocoel. The junction between foregut and intestine is marked by the change in gland cell appearance, presence of food vacuoles in the epithelial cells and sparse ciliation. The anterior portion of the intestine, like the foregut with which it communicates, arches below the rhynchocoel as a wide but compressed tubular canal. Behind the end of the rhynchocoel, however, the intestine enlarges to occupy most of the body space between the gonads and lateral blood vessels and its epithelium is up to 45 lm or more in height. The intestine does not possess lateral pouches or diverticula. Blood system. A pair of spacious lateral cephalic lacunae in the head (Fig. 13) meet anteriorly by a broad transverse connective crossing above the proboscis pore. The lacunae are irregularly crossed by isolated muscle fibres or connective tissue fibrils, so that in some sections there appear to be more than two blood channels. Near the front of the brain the cephalic lacunae meet below the rhynchodaeum by a ventral connective, which continues posteriorly as a median ventral channel. This channel, at least anteriorly, is irregularly subdivided by connective tissue and muscle fibrils. There are three longitudinal lacunae in the brain region; the lateral cephalic lacunae continue back, one on either side of the rhynchodaeum, whereas the ventral lacuna enlarges to occupy much of the ventral half of the body but is separated from the lateral lacunae and rhynchodaeum by the transverse muscle band. Towards the rear of the brain, as the oral epithelium bulges inwards, the ventral lacuna becomes compressed and then separates to form two lacunae, one running on either dorsolateral margin of the foregut. There are thus four lateral blood lacunae, arranged in dorsal and ventral pairs separated by transverse muscles, in the mouth region (Fig. 14). Just behind the mouth, however, the ventral lacunae end blindly. The dorsal lacunae continue on either side of the rhynchodaeum until, just before the proboscis insertion, they become less spacious and move to a dorsolateral position on either side of the foregut, internal to the body wall inner circular muscle layer. They continue in this position for the remaining length of the foregut and anterior intestine but, behind the end of the rhynchocoel, expand again to form a pair of large lateral channels running on either side of the intestine and outside the inner circular muscle layer. There are no pseudometameric transverse connectives nor a median dorsal vessel.
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Nervous system. The cerebral ganglia and lateral nerve cords are situated in the proximal portion of the epidermis. The brain lobes are large and well developed relative to the diameter of the head (Fig. 14). Dorsal and ventral lobes are of similar size, both being incompletely enclosed by a distinct outer neurilemma, which has an appearance of concentric layers of connective tissue fibres. The ventral lobes are located ventrolaterally, the dorsal laterally. Posteriorly the dorsal lobes reach above the mouth (Fig. 14). A distinct inner neurilemma separating the fibrous and neuroganglionic tissues of the brain lobes is also present, though thinner than the outer layer. The ventral cerebral commissure, about 40 lm thick, is anterior to the dorsal commissure, which has a maximum thickness of 15 lm. In front of and behind both commissures, acidophilic glands histologically identical with glands found in the remaining epidermis are distributed between the neuroganglionic cells of the brain (Fig. 14); close anteriorly and posteriorly to the commissures, these glands are also enclosed by the outer neurilemma. Farther from the commissures, their separation from the remaining epidermal tissues becomes less distinct. No evidence of either neurochord cells or neurochords could be found in the brain or lateral nerves. The lateral nerves, whose fibrous cores are 40–45 lm in diameter, extend posteriorly in the proximal epidermis on either side of the body (Fig. 15). A distinct zone of several more or less discrete cephalic nerves extends anteriorly from the front of the brain in the proximal portion of the epidermis (Fig. 13). These nerves can be followed almost to the tip of the head. Among the other peripheral nerves that can be distinguished is a pair of nerves leading posteriorly from the rear of the ventral commissure, and passing on either side of the oral epithelium. The ultimate fate of these nerves could not be followed but they comprise the buccal or foregut nerve supply (Fig. 14). A median dorsal nerve (Fig. 15) leading from the dorsal cerebral commissure can be traced back at the proximal border of the epidermis into the anterior intestinal region. Sensory organs. The present species does not possess eyes. In the cerebral region a wide but shallow indentation on either side of the body leads to a distinct lateral furrow, some 30 lm deep. The cilia of the furrows are long (15 lm) and dense. From the ventral margin of each furrow a ciliated cerebral canal, 15–18 lm in diameter, leads inwards between the dorsal and ventral fibrous cores of the brain lobes, then turns backwards to continue posteriorly for approximately 200 lm before ending blindly. As it extends posteriorly, each canal gradually moves to a more dorsolateral position. Each cerebral canal, throughout its length, is surrounded by neuroganglionic tissues histologically indistinguishable from those of the brain lobes (Fig. 14), and there is no evidence of glandular tissues associated with any part of the canal. These structures constitute the cerebral sensory organs but appear to have a much more simple construction than those of most other nemerteans. No other sensory structures could be distinguished in any part of the body. Frontal glands and apical organ. The present species possesses neither an apical organ nor frontal glands. Excretory system. The excretory system commences in the intestinal portion of the body, close behind the posterior limit of the distinct acidophilic glandular band found in the epidermis. Anteriorly, the system comprises a short glandular mass
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lying close to the lateral blood lacunae; from the rear of this mass a single collecting tubule leads posteriorly for about 200 lm, then turns outwards to form a wide (10–15 lm) efferent canal that leads dorsolaterally to a single nephridiopore on each side of the body. Reproductive system. The single specimen is an immature female. The ovaries are distributed in a single dorsolateral row on either side of the body, dorsal to the lateral blood lacunae, commencing close behind the end of the rhynchocoel. Several ova in different stages of oogenesis are present within each ovary. Systematic discussion. Sundberg & Hylbom’s (1994: fig. 9) phylogenetic analyses show that HK sp. 1 belongs in the same clade as Carinina arenaria Hylbom, 1957, C. atavia (Bergendal, 1902), C. coei Hylbom, 1957, C. grata Hubrecht, 1887, C. remanei (Nawitzki, 1931) and C. wijnhoffae Kulikova, 1984; Carinina grata is the type species for the genus, which currently contains 14 described forms (Gibson, 1995), and there is no doubt that the present form from Hong Kong belongs in the same genus. Reference to the character matrix given by Sundberg & Hylbom (1994: Table 2) shows that HK sp. 1, whilst sharing many anatomical features with the other Carinina species, can be distinguished from all of them. For example, C. buergeri Joubin, 1902, and C. remanei possess two dorsal cerebral commissures; statolith-like structures are present in the brain of C. arenaria, C. buddenbrocki (Friedrich, 1935a), C. coei, C. heterosoma Mu¨ller, 1956, C. poseidoni Friedrich, 1935b, and C. remanei, whilst there are no rhynchodaeal nerves in C. pacifica Friedrich, 1970. Other morphological characters, too, can be used to distinguish the present taxon from one or more of the known Carinina species; these include the number of dorsal nerves, presence of rhynchocoel blood vessels, the organisation of the body wall muscle layers, the position of the lateral blood vessels in relation to the body wall inner circular musculature, and the arrangement of the blood system in the oral region. Differences that can be used to separate the known species of Carinina are summarized in Table 1. It is concluded that the Hong Kong form is new to science, and it is accordingly named Carinina sinensis sp. nov.
Genus Tubulanus Renier, 1804 Diagnosis. The genus Tubulanus, according to Sundberg & Hylbom’s (1994: Table 4) character matrix, contains species with the following anatomical features: length at the onset of sexual maturation 2–10 cm; coloured, usually with a conspicuous pattern; head furrows present; body wall musculature consisting of outer and inner circular and middle longitudinal layers; muscle crosses present between outer and inner circular muscles in some species; diagonal muscles present; cerebral sensory organs consisting of ciliated pits or ciliated canals in the epidermis; side organs present in foregut region in some species; cephalic region with nerve layer; two nerves in rhynchodaeal epithelium; proboscis nerves present; brain and lateral nerves situated between epidermal basement membrane and outer circular muscles; epidermal basement membrane usually thick; nervous system with neither neurochords nor neurochord cells; buccal nerves present and paired; intestine with shallow lateral diverticula; rhynchocoel wall with circular muscles only; proboscis musculature with outer longitudinal and inner circular layers; circular muscle layer in rear end of rhynchocoelic or in nephridial regions
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T 1. Summary of some of the anatomical features that can be used to distinguish between species of the palaeonemertean genus Carinina. Based on data contained in Sundberg & Hylbom (1994) Species of Carinina
A
B
C
D
E
F
G
H
antarctica Bu¨rger, 1904 arenaria Hylbom, 1957 atavia (Bergendal, 1902) buddenbrocki (Friedrich, 1935) burgeri Joubin, 1902 coei Hylbom, 1957 grata Hubrecht, 1887 heterosoma Mu¨ller, 1965 littorea Korotkevich, 1982 mawsoni Wheeler, 1940 pacifica Friedrich, 1970 poseidoni Friedrich, 1935 remanei (Nawitzki, 1931) wijnhoffae Kulikova, 1984 sinensis sp. nov.
? 2 1 2 ? 2 2 1 2 1 1 2 1 1 1
2 1 1 ? ? 1 0 0 1 2 0 1 1 1 0
0 0 0 0 ? + 0 0 + 0 0 0 0 0 0
? 0 0 0 + 0 0 0 ? 0 0 0 0 0 0
? + 0 + ? + 0 + ? ? 0 + + 0 0
? 0 0 ? ? 0 0 + ? 0 0 ? 0 + 0
? 1 1 1 2 1 1 1 ? ? ? 1 2 1 1
? 0 1 ? ? 1 0 0 ? 0 2 2 2 1 2
A: B: C: D: E: F: G: H:
Median dorsal nerve supply consisting of upper nerve only (1) or with both upper and lower nerves (2). Lateral blood vessels anteriorly run internal to body wall inner circular muscle layer but further back move outside these muscles (0), remain entirely internal to inner circular musculature (1) or are completely external to the muscle layer (2). Rhynchocoel blood vessels present (+) or absent (0). Eyes present (+) or absent (0). Statoliths in cerebral ganglia present (+) or absent (0). Cephalic glands present (+) or absent (0). Dorsal cerebral lobes transversely linked by one (1) or two (2) dorsal commissures. Blood system in mouth/anterior foregut region consisting of two lateral vessels only (0), lateral vessels developed to form vascular plexus around foregut (1) or with four lateral vessels not forming plexus (2).
strongly developed; gland-like anterior part of excretory system entering lateral blood vessels; blood vascular system without mid-dorsal vessel; eyes absent; sexes separate. Body wall muscle crosses and the presence of proboscis nerves are regarded as possible synapomorphies by Sundberg & Hylbom (1994). This diagnosis broadly agrees with the traditional definition of the genus given by Gibson (1994), although certain additional characters included by Gibson are shown in italics in the diagnosis above. Tubulanus hylbomi sp. nov. (Figs 16–20) HK sp. 5 in Sundberg & Hylbom (1994) Type specimens. Holotype: immature, series of transverse sections through anterior body back to intestinal region, (13 slides), paratypes: immature, series of transverse sections through anterior body region, (19 slides) and through anterior body back to intestinal region, (18 slides), SMNH 4893. Type locality. South-east of Tap Mun, 17 April 1992, trawled from 33 m depth in fine clay (Taylor, 1992: Trawl 13 [Location 2, Fig. 1]). Additional locations. South-east of Tap Mun, 28 April 1992, trawled from 5 m depth in rubble and mud (Taylor, 1992: Trawl 51 [Location 3, Fig. 1]), and intertidal in mud at Hoi Ha Wan (Location 1, Fig. 1).
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Figure 16. Tubulanus hylbomi sp. nov. Drawing to show the cephalic lobe and anterior colour pattern, viewed dorsally, based on sketches made of a living specimen.
Etymology. The species is named after Richard Hylbom as a tribute to his work on palaeonemerteans. External features. Two of the three specimens obtained were fragmented. The only intact individual was about 35 cm long, with a maximum width of 3 mm. The body was somewhat flattened in cross-section, with the dorsal surface more rounded. The head was clearly demarcated from, although the same width as, the adjacent portion of the body, which gradually tapered posteriorly. The general colour was a light brown, marked with two lateroventral longitudinal white stripes which anteriorly extended to the rear of the head, and a median dorsal white stripe which almost reached the cephalic tip (Fig. 16) and here formed a cross. The margins of the head were also white and unevenly spaced white bands were present throughout the length of the body, commencing about 2 cm behind the head. A white band immediately in front of the mouth, which had white borders, demarcated the posterior limit of the head. Neither eyes nor cephalic furrows were visible in life, although the proboscis pore was distinguishable near the anterior tip of the head. Body wall, musculature and parenchyma. The epidermis is mostly 150–170 lm thick, but tends to be much less than this along the lateral body margins or where locally folded. Coarsely granular acidophilic glands are scattered throughout the epidermis in the head and foregut regions but farther back form an almost continuous layer, 30–75 lm deep, encircling the body; the glands, with tracts of secretion extending to the epidermal surface, are mainly situated proximally but are separated from the epidermal basement layer by a clear zone about 30 lm wide. These acidophils are completely missing from the extreme anterior cephalic region and posterior to the excretory pores. At least two other types of epidermal glands can be distinguished, one basophilic with homogeneous to finely particulate contents, the other finely granular and staining with Orange G; neither of these gland types, however, forms
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Figure 17. Tubulanus hylbomi sp. nov. Camera lucida drawing of transverse section through the cephalic region to show the well developed cephalic glands, rhynchodaeum and blood system.
a distinct layer, instead being widely scattered between the proximal and distal portions of the epidermis. The connective tissue epidermal basement layer, mostly 5–30 lm thick depending upon local contraction, has a proximal mesh-like appearance and distally extends into the basal portion of the epidermis. Along the lateral cephalic margins this basement layer is often so delicate as to be almost indiscernible (Fig. 17). The body wall musculature comprises outer circular, middle longitudinal and inner circular layers which are respectively some 15–30 lm, 100–150 lm and 3–15 lm thick. The longitudinal muscle fibres are arranged into fasciculated bundles. The inner circular muscles laterally and ventrally surround the foregut and intestine, but dorsolaterally merge with the circular muscles of the rhynchocoel wall (Figs 18, 19). A plate of horizontal longitudinal muscles, up to about 45 lm thick above the gut, extends between the rhynchocoel and gut walls. The fibres forming this layer also extend around the foregut wall between its epithelial basement membrane and the inner circular musculature (Fig. 18), but are here very much more weakly developed, rarely more than 6–8 lm deep, and ventrally are reduced to small isolated fibre bundles adjacent to the foregut wall. These horizontal muscles split up above the anterior part of the mouth, forming isolated bundles of fibres that become separated from the oral epithelium by bands of transverse muscles up to 35–40 lm thick; these transverse muscles have their origin among the proximal lateral fibres of the body wall longitudinal musculature. No muscle crosses were found between the outer and inner body wall circular muscle layers, as reported for several species of Tubulanus. In the head, the two outermost body wall muscle layers are significantly reduced, the circular layer to about 15 lm in maximum thickness, the longitudinal layer to between 7–45 lm. The inner circular musculature also extends into the head, where it forms a transverse plate of fibres 7–15 lm across passing below the cephalic blood lacunae and between the frontal gland lobules; only mid-ventrally does this muscle layer run adjacent to the longitudinal musculature. Parenchymatous connective tissues are moderately extensive, particularly on either side of the foregut, anterior intestine and rhynchocoel.
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Figure 18. Tubulanus hylbomi sp. nov. Camera lucida drawing of transverse section through the foregut region.
Figure 19. Tubulanus hylbomi sp. nov. Camera lucida drawing of transverse section through the anterior intestinal region.
Proboscis apparatus. The proboscis pore opens subterminally. It leads into a tubular rhynchodaeum whose ciliated epithelium is at first histologically similar to the adjacent epidermis, except for lacking gland cells. Behind the proboscis pore the rhynchodaeal epithelium varies from 15 to 75 lm in thickness, depending upon the
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degree of folding, but farther back in the head becomes progressively compressed by the development of the frontal glands and is in places less than 2–3 lm across. The posterior portion of the rhynchodaeum is identical in appearance to the frontal glands situated immediately beneath its epithelium, but under high power a delicate basement membrane can often be distinguished separating the rhynchodaeal epithelium from the glands. The rhynchodaeum is surrounded by a layer of longitudinal muscle fibres (Fig. 17). The proboscis insertion is situated in the posterior cerebral region, close to the rear of the brain. The rhynchocoel wall contains only circular muscle fibres (Figs 18, 19), forming a distinct layer up to 45 lm or more thick. In the foregut region, the rhynchocoel occupies about 60% of the body diameter. The proboscis for most of its length is about 800 lm in maximum diameter when retracted. It is composed of a columnar epithelium 150 lm or more tall, an outer circular muscle layer 20–35 lm across, an inner longitudinal muscle layer 35–45 lm thick, and an inner lining layer (Fig. 18). The epithelium distally bears scattered ‘pads’ of basophilic rhabditoids about 5–6 lm tall and 15 lm in diameter; the pads are often arched in a semi-circular shape. There are two proboscis nerves, one on either side of the organ situated between the epithelium and circular muscle layer (Fig. 18); these nerves are not always distinguishable in the more posterior parts of the proboscis (Fig. 19). Scattered Orange G positive glands occur in the proximal half of the epithelium. The extreme anterior end of the proboscis is slightly wider than the remainder of the organ and, in places, is almost 1 mm in diameter. The epithelium lacks the rhabditoid pads in this region. The proboscis nerves arise from the inner face of the dorsal brain lobes. Alimentary canal. The mouth opens immediately behind the brain, although the oral groove in the epidermis extends forwards below the posterior brain region. The oral margins may protrude ventrally some 400 lm to give the appearance of thick ‘lips’. The buccal epithelium is folded, 90–150 lm or more tall, clad in short densely distributed cilia and richly provided with gland cells which are mainly basophilic. The foregut is spacious and for much of its length possesses deeply folded walls on all but the dorsal margin (Fig. 18); here, below the rhynchocoel, the epithelium is only 60–70 lm thick and not folded. Both the epithelial height and degree of folding are progressively reduced posteriorly, at the same time as the density of the basophilic gland cells is also diminished. The junction between foregut and intestine is marked by the appearance of long, sparsely distributed cilia and pyriform gland cells. The intestinal wall is mostly 100–140 lm thick. The intestine does not possess lateral diverticula and for much of its length forms a spacious, but somewhat dorsoventrally compressed, canal arching beneath the rhynchocoel (Fig. 19). Blood system. In the head a well developed lacunar network, flanking the rhynchodaeum, comprises a pair of large lateral channels which are irregularly subdivided by muscle and connective tissue fibrils (Fig. 17). Branches of the lacunae also extend and meet above the rhynchodaeum. Anteriorly, the lacunae meet by a slender transverse dorsal connective situated close behind the proboscis pore. Two large lateral lacunae enter the cerebral ring close to the inner borders of the brain lobes, but smaller dorsolateral branches are still present adjacent to the rhynchodaeal wall. Behind the ventral cerebral commissure, an outer ventrolateral lacuna appears on each side of the body in the parenchyma between the epidermal basement layer
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Figure 20. Tubulanus hylbomi sp. nov. Camera lucida drawing of transverse section through the cerebral region. Note the blood vessels running close to the cerebral sensory organs.
and the brain lobes (Fig. 20). These lacunae are spacious, up to 230–250 lm or more in maximum dimension, and are irregularly traversed by connective tissue and muscle fibrils. Farther back, as the cerebral sensory organs appear, the lacunae are divided into upper and lower branches by the cerebral organ nerve leading from the brain (Fig. 20). The lower branch on each side of the head runs close to the cerebral organ and is filled with a mixture of finely granular basophilic, coarsely granular acidophilic and vacuolar acidophilic material that appears to be secretory, rather than representing typical blood cells, as described from many other nemertean species; it is possible that this material is derived from the glands of the cerebral organs although the lacunae, whilst passing close to the organs, do not seem to have intimate contact with them. The two branches of the ventrolateral lacunae, towards the rear of the brain, meet to form a spacious channel which is further subdivided by muscle and connective tissue strands; branches of these lacunae are in connection with the main lateral blood channels, which continue back from the cephalic blood supply. In front of the mouth the blood system comprises a pair of large lateral lacunae flanking the rhynchocoel and buccal walls. Behind the mouth, further subdivision of the lacunae by connective tissue and muscle fibrils leads to the development of a foregut lacunar plexus (Fig. 18); this extends throughout the length of the foregut and into the anterior intestinal region. There is no mid-dorsal blood vessel, but a short distance behind the mouth branches of the main lateral lacunae lead towards and penetrate the ventrolateral rhynchocoel floor on either side. The rhynchocoel bodies (i.e. tissue protrusions enclosing blood vessels which penetrate the rhynchocoel wall) so formed have a flattened and rather lozenge-shaped appearance in sections and are about 15 lm by 75 lm in height and width respectively; they run back in the rhynchocoel wall for some 60–80 lm and then appear to end blindly. The vessels in these rhynchocoel bodies contain material similar to that seen in the lacunae adjacent to the cerebral organs. The blood system in the intestinal region essentially comprises a pair of large
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lateral lacunae, lined by an internal epithelium which is in places 15 lm or more thick. These lacunae, too, are sometimes subdivided by tissue strands, but for most of their length form single spacious channels on each side of the body (Fig. 19). No evidence of pseudometameric transverse connectives linking the lateral lacunae could be found in the intestinal region. Nervous system. The large and well developed brain lobes are situated ventrolaterally (Fig. 20). They are enclosed by a distinct connective tissue outer neurilemma, but there is no inner neurilemma separating the neuroganglionic and fibrous cerebral components. For most of their length the brain lobes are separated from the epidermal basement layer by discrete bundles of longitudinal muscle fibres, in places up to 40 lm thick, but these muscle bundles are missing below the ventral commissure and from the lateral brain margins. The single ventral commissure, 45–50 lm thick, is located anterior to the two dorsal commissures, both of which are much longer than the ventral and about 30 lm thick. All three commissures are located in front of the proboscis insertion. Several large nerve tracts can be distinguished emerging from the brain lobes. One pair, extending from the inner anterior surface of the dorsal lobes, forms the origin of the proboscis nerve supply; another pair, emerging somewhat farther back, forms the buccal nerves; and a third pair, leading from the outer ventrolateral surface of the dorsal lobes, innervates the cerebral sensory organs. Several nerves also lead anteriorly from both dorsal and ventral ganglia to form the cephalic neural layer, that extends between the outer circular muscle and the epidermal basement layers (Fig. 17); some of the nerves in this layer are 50 lm or more in diameter. The cerebral organ nerves fork into upper and lower branches soon after leaving the brain and enter the cerebral organs on their dorsal and ventral margins respectively. The dorsal and ventral brain lobes separate a short distance in front of the mouth, but the upper lobes continue posteriorly for some distance before terminating above the oral rim. The lateral nerve cords extend between the body wall outer circular muscles and the epidermal basement layer (Figs 18, 19). Neither the lateral nerves nor the brain lobes contain neurochord cells or neurochords. There is only a single, small, median dorsal nerve, external to the outer circular musculature, and the lower dorsal nerve found in many Tubulanus species could not be discerned. The large and distinct foregut nerves meet above the mouth by a single transverse commissure, 15 lm thick, before branching to form the foregut neural plexus. Several distinct nerves can be traced throughout the foregut length, running adjacent to the epithelial basement membrane (Fig. 18). Sensory organs. The present species does not possess eyes. The cerebral sensory organs, situated in the proximal portion of the epidermis, are large and distinct. Each opens to the exterior via a short ventrolateral ciliated canal leading inwards from the epidermal surface, located at a level just in front of where the dorsal and ventral cerebral lobes separate posteriorly (Fig. 20). The organs are large, up to about 170 lm in diameter and 420–450 lm long, posteriorly ending level with the front of the mouth. For most of their length the organs consist of neural tissues through which the ciliated cerebral canal extends directly backwards; proximal major and distal minor channels, similar to those described for several other nemertean species, are clearly visible in transverse section. Glandular components of the organs are mainly anterodistal in position and irregularly extend into the adjacent
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epidermis; there is no basement membrane separating the cerebral organs from the other epidermal tissues. Deep narrow longitudinal ciliated furrows on the head, not distinguishable in life, are somewhat variable in their position and appear to represent localized foldings of the body surface rather than having any sensory significance. Lateral sensory organs, reported from several species of Tubulanus, could not be found in the present form and no other sensory structures were found. Frontal glands and apical organ. The frontal glands are extremely extensive and fill most of the head between the proboscis pore and cerebral ganglia; some of the glands reach as far back as the mouth. The glands are arranged into large, irregularlyshaped and sized lobules (Fig. 17) filled with finely homogeneous and lightly basophilic cytoplasm. For much of the cephalic region the rhynchodaeal epithelium is histologically identical in appearance and in places appears to connect with these glands. The glands discharge to the exterior through the apical organ, which opens into the dorsal wall of the rhynchodaeum above the proboscis pore. The apical organ is more or less spherical, 75–90 lm in diameter and surrounded by a delicate layer of longitudinal muscle fibres. Excretory system. The excretory system is situated dorsolaterally in the anterior intestinal region of the body; the collecting tubules, mostly up to about 60 lm in diameter, are lined by an epithelium some 15 lm thick. The tubules run in the parenchyma between the body wall longitudinal musculature and lateral blood lacunae. In some sections there appear to be several smaller tubules on each side, whilst in others they unite to form one or two large ducts 150 lm or more in diameter. In the anterior region thin-walled pouches on either side protrude into the lacunar wall from the collecting tubules. Towards the rear of the system the collecting tubules lead to a large thin-walled chamber, in places more than 200 lm across, from which short but thick-walled efferent canals, some 45 lm in diameter, lead dorsolaterally to open via the nephridiopores. There appears to be only a single nephridiopore on each side of the body. Reproductive system. None of the specimens contained mature gonads, although in one individual small and isolated flask-shaped pouches, located dorsolaterally in the parenchyma of the intestinal region (Fig. 19) are apparently gonads. Evidence of ducts leading from these structures towards the body surface suggests that the individual might be post-spawning, but the sexuality of the species remains unknown. Systematic discussion. The present species forms a clade with several other Tubulanus, including the type species for the genus (Tubulanus polymorphus Renier, 1804) in the phylogeny of Sundberg & Hylbom (1994: Fig. 4). Since it possesses several anatomical features that are traditionally associated with the taxon, we place the Hong Kong form in the genus Tubulanus. A comparison between the characters and their states for the 11 species shown in Sundberg & Hylbom’s (1994: Table 2) character matrix table shows that, excluding the present form, all the taxa share the following features, apart from those for which a particular character state is unknown (listed in parentheses): the head is bluntly rounded and possesses neither eyes (no data for T. nothus, although it is probably eyeless) nor cephalic sensory pits; the thickness of the epidermis relative to the body diameter in the midgut region is >0.05; the body wall musculature comprises outer circular, middle longitudinal and inner circular layers; the cerebral
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sensory organs are situated in the epidermis; excretory organs are present with the canal outside the body wall inner circular muscle layer (no data for T. floridanus Coe, 1951); there are neither neurochord cells nor statoliths in the brain lobes; the head possesses a well developed neural layer rather than four large and distinct nerves (no data for T. punctatus); proboscis nerves are present; the proboscis insertion is situated in the brain region (no data for either T. floridanus or T. punctatus); the proboscis musculature comprises outer circular and inner longitudinal layers; the rhynchodaeal epithelium is glandular; the rhynchocoel is less than the full body length (not recorded for T. capistratus or T. superbus); the brain and lateral nerve cords are situated between the epidermal basement layer and the body wall outer circular muscles; the ventral cerebral commissure is thicker than the dorsal; finally, the intestine does not possess lateral diverticula (no data for T. floridanus or T. punctatus). The present species also shares most of these features, although in their table 2 Sundberg & Hylbom (1994) indicate that in HK sp. 5 the proboscis insertion is located behind, rather than in, the brain region (Character 42, State 2); in the present studies it is evident that the insertion is positioned in the posterior cerebral region and a distinction between States 1 and 2 for this character becomes less obvious and is not regarded as necessarily significant. One feature found in the present species, however, differs from that described for the other palaeonemerteans in this group, namely that an incomplete layer of longitudinal muscle fibres is present between the brain lobes and the epidermal basement layer. Gibson (1995) lists 30 species of Tubulanus currently regarded as valid, 19 of which are known to possess a distinct colour pattern (there is no information on the external features of T. holorhynchocoelomicus Friedrich, 1958), though not all are either fully or adequately described. The body coloration of the nine Tubulanus species being compared with the present form are summarized in Table 2. The colour pattern of the Hong Kong species differs from that reported for most of these in that T. polymorphus and T. theeli are uniformly coloured with neither longitudinal stripes nor transverse bands, Tubulanus floridanus and T. rubicundus have transverse bands but no longitudinal stripes, T. punctatus and T. superbus possess four longitudinal stripes including a median ventral one, and T. nothus has a characteristic colourless head marked with a pair of black patches. The present species can be distinguished from the remaining two taxa in that T. annulatus possesses muscle crosses between the two body wall circular muscle layers and has both upper and lower dorsal nerves, whilst T. capistratus has lateral sensory organs, no buccal nerves and both circular and longitudinal muscle layers in its rhynchocoel wall. Reference to Sundberg & Hylbom’s (1994: table 2) character matrix for all of the species listed in Table 2 that differ from the present form in colour pattern shows that they also differ in several anatomical features from the Hong Kong taxon, which is accordingly described as a new species, Tubulanus hylbomi. Tubulanus longivasculus sp. nov. (Figs 21–23) HK sp. 6 in Sundberg & Hylbom (1994) Type specimens. Holotype: mature female, series of transverse sections through the anterior end of the body (27 slides), paratype: mature male, series of transverse sections through the foregut/intestinal region (23 slides), SMNH 4894.
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T 2. Summary of the body coloration of the nine species of Tubulanus being compared with the present species from Hong Kong Species
Coloration
Tubulanus annulatus
Overall colour vivid brick-red, orange-red, garnet-red or brownish-red, marked with mid-dorsal and lateral longitudinal white stripes and transverse white bands; ventral surface paler than dorsal and, apart from the first 2–3 bands, all are more or less equidistantly spaced. Cephalic lobe with transverse white band. Overall colour rich deep brown or greyish-black, posteriorly paler and yellowishbrown, with slender mid-dorsal and lateral longitudinal white stripes, lateral stripes much broken up anteriorly, with 200 or more transverse white bands. Overall colour brown with series of very narrow transverse bands, most of which completely encircle the body, without longitudinal stripes. Head colourless, marked with pair of crescentic black patches near anterior margins, dorsal body dark reddish-brown, ventral paler orange-brown fading to yellowish anteriorly and posteriorly. White dorsal median and lateral stripes present, usually with an inconspicuous median ventral stripe too. Forty or more white bands encircle body, occasional bands doubled, first three situated some distance in front of remainder. Body uniformly reddish- or orange-brown, paler towards posterior, without colour pattern. Body generally blackish-brown, sometimes chestnut-brown or brownish-yellow, fading posteriorly, ventral surface paler than dorsal. White band across head sometimes appearing as row of dots. With numerous transverse white bands more or less equidistantly spaced, bands mostly broad and narrow rings alternating. With mid-dorsal, mid-ventral and lateral white dotted longitudinal stripes, though these tend to be somewhat obscure. Dorsal and ventral body surfaces strongly coloured cherry-red, sometimes with purplish or fire-red tinge dorsally. Middle of head marked with pale yellow bar and pale yellow margins. Similar narrow pale yellow band behind mouth, followed after 10–12 mm by second band twice as thick, then after about 20 mm thicker and thinner bands alternate along body at intervals of about 4 mm. Under high power, groups of bands can be seen to consist in turn of very thick, thin, moderately thick, thin and very thick bands in regular sequence. General colour rich dark brown, reddish-brown, scarlet or cherry-red, with middorsal, mid-ventral and lateral longitudinal white or yellowish-gold stripes and large numbers (up to 200 or more) transverse white bands. Occasional bands may appear doubled, first three bands widely spaced, remainder close together and more or less equidistant. Body uniformly dark reddish-brown, without colour pattern.
Tubulanus capistratus Tubulanus floridanus Tubulanus nothus
Tubulanus polymorphus Tubulanus punctatus
Tubulanus rubicundus
Tubulanus superbus
Tubulanus theeli
Type locality. Western side of north tip of Flat Island (Location 4, Fig. 1), collected by SCUBA diving by PS, 7 m depth on fine to medium shelly sand with some mussel beds on top; the specimen was creeping about on the sediment surface. Erymology. The specific epithet, a composite of the Latin words longus (long) and vas (a vessel), refers to the unusually long rhynchocoelic blood vessel of the species. External characters. The single complete specimen obtained was more than 60 cm long. The rounded head was clearly demarcated from the remainder of the body and bore cephalic furrows which, though not evident in life, are clearly distinguishable in histological preparations. The general colour was brown, paler ventrally, marked
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Figure 21. Tubulanus longivasculus sp. nov. Drawing to show the colour pattern and appearance of the anterior end of the specimen.
Figure 22. Tubulanus longivasculus sp. nov. Camera lucida drawing of transverse section through the foregut region.
with two distinct pale brown dorsal longitudinal stripes (Fig. 21). There were also indistinct transverse bands and the lateral body margins were white. Body wall, musculature and parenchyma. In the foregut region the epidermis varies between 200 and 350 lm or more in height (Fig. 22) but is less than this in the
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Figure 23. Tubulanus longivasculus sp. nov. Camera lucida drawing of transverse section through the cerebral region. Note the bundles of longitudinal muscle fibres which intrude between the cerebral ganglia and the epidermal basement layer.
cephalic and posterior body regions. Several types of epidermal glands can be distinguished, arranged into distal and proximal zones. Strongly positive acidophilic glands, forming a dense proximal ‘layer’ encircling the body and extending for more than half the epidermal height, first appear in the foregut region at about the level of the rhynchocoel bodies (see Blood system, below). Their number gradually diminishes posteriorly. The connective tissue basement layer, with a finely striated appearance and radially orientated mesh-like fibres, is in places up to 90 lm or more thick (Fig. 22). A thin but distinct darker-staining membrane interfaces between the epidermis and this layer. Radial connective tissue fibres extend from the basement layer for up to about 60 lm into the epidermis at more or less regular intervals around the body. The body wall musculature comprises outer circular, middle longitudinal and inner circular layers (Fig. 22). In the foregut region these are respectively some 30 lm, 230 lm and 45–50 lm across, whereas in the intestinal regions the widths of these muscle coats are in comparison some 15–25 lm, 180–190 lm and 100 lm at most. A horizontal plate of longitudinal muscle fibres, 45–50 lm thick, extends between the gut and rhynchocoel; these muscles continue around the foregut between the gut epithelium and body wall inner circular muscle layer (Fig. 22) but laterally and ventrolaterally tend to be thinner (10–15 lm) and are ventrally arranged in isolated bundles of fibres running in the parenchyma. The muscle layer posteriorly reaches well into the intestinal region. Above the mouth the horizontal muscles break up into separate bundles, ventrolateral and lateral to the proboscis insertion, and are separated from the buccal wall by a loose layer of transverse muscle fibres crossing the body between the proximal portions of the body wall longitudinal musculature. The bundles of longitudinal fibres continue in front of the mouth, gradually expanding dorsoventrally until in the brain region they form a distinct but dorsally incomplete layer flanking the proboscis insertion (Fig. 23). The layer
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continues anteriorly into the head, extending on either side of the rhynchodaeum, where it ventrally merges with the blocks of body wall longitudinal muscles that run anteriorly from between the brain lobes. The longitudinal muscles running next to the rhynchodaeum are up to 60–70 lm thick but farther forwards are less strongly developed. In the head, outer circular and middle longitudinal body wall muscle layers are respectively about 15 lm and 45 lm in maximum thickness, and there is no trace of the inner circular musculature. Delicate bundles of dorsoventral fibres cross the head between the frontal gland lobules. Parenchymatous connective tissues are moderately extensive throughout the postcerebral regions of the body. Proboscis apparatus. The proboscis pore is subterminal. It opens into a rhynchodaeum whose wall is at first densely ciliated, without glands and 45–60 lm thick, but soon after the proboscis pore closes the epithelium becomes more sparsely ciliated and contains gland cells that are histologically identical with those making up the frontal gland lobules. In the more posterior parts of the rhynchodaeum these lightly basophilic glands are predominantly confined to the dorsal half of the epithelium. Occasional small, scattered acidophilic glands are also evident in the posterior rhynchodaeal epithelium. The proboscis insertion is situated in the brain region, behind the ventral cerebral commissure. A pair of nerves, one arising from the inner margin of each ventral cerebral ganglion close behind the ventral commissure, provides the origin of the proboscis nerve supply. The rhynchocoel does not reach the posterior half of the body. Its wall contains only a circular muscle layer which, in places, is up to 90 lm or more thick (Fig. 22). The muscle fibres, particularly in the foregut region, are loosely arranged in contrast to the intestinal region where they are more compact and the muscle layer is reduced to a thickness of about 45–50 lm. The connective tissue basement layer encircling the rhynchocoel is anteriorly 15 lm across, posteriorly only about 2–3 lm. The width of the rhynchocoel relative to the body diameter varies; above the mouth it is only about 10% of the body diameter, but behind the mouth rapidly increases to some 35% and, posterior to the level of the rhynchocoelic bodies, is mostly 50% or more of the body width. The proboscis is regionally differentiated. Its anterior portion, some 400–425 lm in overall diameter when retracted, comprises an epithelium 30–45 lm tall which contains few gland cells and is developed into four distinct longitudinal ‘welts’ of tissue. The two distinct proboscis nerves, which are about 60 lm in maximum dimension, are situated on opposite sides of the organ between the epithelial basement membrane and the proboscis musculature; they tend to protrude distally and so distort the epithelium towards the proboscis lumen. Below both the epithelium and the nerves a connective tissue layer intervenes before the longitudinal musculature, which is up to about 90 lm thick and is followed in turn by a thick inner connective tissue layer and a flattened inner lining. No circular muscles can be distinguished in this portion of the proboscis. For most of its length, in contrast, the proboscis is about 500 lm in diameter and composed of a glandular epithelium 65–70 lm tall, a thin outer connective tissue layer, an outer circular muscle coat 15–25 lm wide, an inner longitudinal muscle layer about 70 lm in maximum thickness, an inner connective tissue zone and a lining layer (Fig. 22). No rhabditoid glands could be found in the proboscis epithelium. In the posterior region of the
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proboscis, 550–600 lm in maximum diameter, the epithelium is reduced to a height of only 15–45 lm and contains fewer glands, the two nerves are very much flattened, smaller and less distinct, the longitudinal musculature has a maximum width of only 40–45 lm and the inner connective tissue zone, though remaining distinct, is very thin. Alimentary canal. The small mouth opens below the rear of the brain. The foregut epithelium, up to about 60 lm thick, is dominated by basophilic gland cells and, except on its dorsal margin, tends to be deeply folded (Fig. 22). The density of the glands gradually decreases posteriorly. The foregut nerve supply is well developed; it consists of 10–17 nerves arranged in a plexus, running either immediately outside the foregut epithelial basement membrane in the parenchyma or, more commonly, between the basal region of the epithelial cells and their basement membrane. The nerves can be distinguished on all sides of the foregut. The junction between foregut and intestine is marked by a change in gland cell type and density and by the more sparsely distributed cilia of the gastrodermis. The intestinal epithelium is not folded, has a thickness of 90–150 lm and lacks lateral diverticula. Blood system. In the anterior part of the head a pair of spacious lateral lacunae connect above the rhynchodaeum by an equally spacious transverse connective. Both the lateral lacunae are irregularly subdivided by muscle and connective tissue fibrils. The cephalic lacunar network extends throughout the head region but, farther back where the rhynchodaeum is dorsoventrally extended, the dorsal portions of the network are missing. The cephalic lacunae remain spacious as they pass through the brain region (Fig. 23), behind the proboscis insertion expanding to almost completely surround the anterior portion of the rhynchocoel except where the buccal wall protrudes from the ventral margin. In the oral region the two large lateral lacunae are irregularly crossed by connective tissue and muscle strands, but towards the rear of the mouth begin to become increasingly subdivided to form a plexus of smaller channels which extend back along the lateral and ventral margins of the foregut (Fig. 22). The branches of the plexus run in the parenchyma between the body wall longitudinal and inner circular muscle layers. On each side of the body the most dorsal channel, often close to the lateral wall of the rhynchocoel, remains consistently larger than and often fuses with other branches of the plexus. In the more posterior part of the foregut the plexus becomes reduced in complexity, and the branches are both smaller in size and tend to have thicker walls. In several places throughout the length of the foregut vascular plexus, slender canals lead off from the most dorsal channel on each side, pass through the rhynchocoel muscle layer and penetrate the lateral rhynchocoel wall to lead to the two rhynchocoel bodies (Fig. 22). These are exceptionally long, extending back in the rhynchocoel wall for some 3.9 mm and reaching into the intestinal region of the body. The length of these rhynchocoel bodies far exceeds that reported for any other species of Tubulanus and their arrangement is more like the rhynchocoelic villus described from many heteronemerteans. They have a multicellular, acidophilic appearance and are mostly somewhat triangular in shape, their distal surface being distinctly flattened. Their form varies; in some sections the rhynchocoel bodies are up to 110 lm wide but only about 15–20 lm in height, whereas in others they are 80–90 lm tall but only 60–75 lm wide. Finely granular acidophilic material distinguishable in the vessels extending through the rhynchocoel bodies can also be
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seen in the canals leading between the blind-ending bodies and the dorsal branches of the foregut vascular plexus. The arrangement of the blood supply in the intestinal region is similar to that described above for Tubulanus hylbomi sp. nov. Nervous system. The large and well developed cerebral ganglia (Fig. 23) possess an outer, but no inner, neurilemma. As in Tubulanus hylbomi sp. nov., bundles of longitudinal muscle fibres run between the epidermal basement layer and the lateral and ventrolateral margins of the brain (Fig. 23), but do not extend below the ventral cerebral commissure. The body wall outer circular muscle layer, although extending alongside the lateral cerebral borders, is also missing ventrally. The ventral commissure is about 115 lm thick, whereas the single dorsal commissure, which crosses the body above the anterior oral region, is only 40–46 lm wide. No evidence of neurochord cells could be distinguished in any part of the brain. The neural layer in the head is well developed. It consists of large numbers of distinct nerves that are very variable in size but with a maximum dimension of some 75 lm. Several other stout nerves can be distinguished. The proboscis nerves emerge from the inner surface of the ventral cerebral ganglia and enter the proboscis insertion through its ventrolateral margin. A pair of large nerves, in places 130–140 lm wide, leads back from the ventral brain lobes to form the buccal nerve supply. The buccal nerves are transversely joined by a slender commissure above the front of the mouth, then pass on either side of the mouth before branching to form the foregut nerve plexus. There is only a single dorsal nerve, up to 60 lm in diameter, running between the body wall outer circular muscle layer and the epidermal basement layer (Fig. 22). Each of the cerebral sensory organs is, as in Tubulanus hylbomi sp. nov., served by dorsal and ventral nerves but in the present species these lead separately from the respective brain lobes, rather than branching from a single nerve. Sensory organs. The present species does not possess eyes, and no trace of the lateral sensory organs reported in some species of Tubulanus could be distinguished. The cerebral sensory organs are situated in the basal portion of the epidermis, between the dorsal and ventral cerebral ganglia, towards the rear of the brain region. They have a maximum diameter of about 150 lm and extend back for some 240 lm. The ciliated cerebral canal, in which both major and minor ciliated canals are easily distinguishable, open laterally in front of the cerebral organs to enter them through their anterior margins. The canals continue directly backwards but, near the posterior limits of the cerebral organs, turn transversely to form a chamber some 45 lm across. The canals are surrounded by neuroganglionic tissues which are in turn almost completely enclosed by gland cells; the latter also extend into the adjacent epidermal tissues. As in Tubulanus hylbomi sp. nov., there are two cerebral organ nerves, but in the present form dorsal and ventral nerves entering each cerebral organ emanate from the respective cerebral ganglia, rather than from a single nerve which then forks. Frontal glands and apical organ. The apical organ forms a long tubular chamber, 90 lm or more in diameter, opening into the front of the proboscis pore epithelium. It extends posteriorly for a short distance above the rhynchodaeal epithelium. The frontal glands are extensive and possess a typical lobular arrangement, although they are not as abundant as in Tubulanus hylbomi sp. nov. The glands extend
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back to the anterior brain region but do not, as in Tubulanus hylbomi sp. nov., reach the proboscis insertion. Excretory system. The nephridial tubules, situated in the anterior intestinal region of the body, run in the parenchyma above the lateral blood vessels outside the body wall inner circular muscle layer. No evidence of an anterior gland-like region to the excretory system, as described for some species of Tubulanus, could be distinguished. The excretory tubules discharge via a single nephridiopore on either side of the body. Reproductive system. The gonads are distributed in bundled groups along the lateral margins of the body. The sexes are separate and were mature at the time of collection (April). Systematic discussion. Sundberg & Hylbom (1994: fig. 9) showed that two of the palaeonemertean species included in their phylogenetic analyses, HK sp. 5 (described above as Tubulanus hylbomi sp. nov.) and HK sp. 6 (the present taxon) are closely related, although certain morphological differences can be distinguished between them (ibid.: table 2). In their figure 12 both of these Hong Kong tubulanids, together with nine previously described species, form a discrete clade (Sundberg & Hylbom, 1994) and the present form can clearly be included in this genus. The colour pattern of HK sp. 6 differs from that of each of these nine taxa (Table 2) as well as from that described above for Tubulanus hylbomi sp. nov., but one unique anatomical feature of the form, regarded as a synapomorphy for the taxon, is the unusual length of the rhynchocoel bodies; this is far greater than reported for any other species of palaeonemertean. Other features also enable the present species to be distinguished from other members of the clade; for example, all the species except for Tubulanus capistratus, Tubulanus floridanus and Tubulanus hylbomi sp. nov. possess muscle crosses between their body wall inner and outer circular muscle layers (Sundberg & Hylbom, 1994: table 1, Character 11), and whereas the present form has only a single, upper, median dorsal nerve (Sundberg & Hylbom, 1994: table 1, Character 27), Tubulanus annulatus, Tubulanus nothus, Tubulanus polymorphus, Tubulanus rubicundus, Tubulanus superbus and Tubulanus theeli each possess both upper and lower dorsal nerves. It is thus concluded that the present taxon is a new species, for which the name Tubulanus longivasculus is proposed.
KEY TO THE PALAEONEMERTEANS OF HONG KONG
The following key, primarily based upon features distinguishable in the living nemerteans, is intended for field use. Some of the species, however, cannot be reliably separated by their external characters alone; for these taxa internal distinguishing features that can only be determined through the use of histological methods are provided in italics within parentheses. 1. 1a.
With distinctive colour pattern consisting of longitudinal stripes, with or without transverse bands ...............................................................................2 Without colour pattern, body more or less uniformly coloured throughout, although tip of head or anterior region may be suffused with darker pigmentation than remainder of body ..........................................................5
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Colour pattern consisting of 2 or 3 longitudinal stripes, with or without transverse bands.............................................................................................3 Tip of head white, general body colour pale yellowish-white to light fawn, marked with 2 dorsal and 3 ventral light brown longitudinal stripes, the former both wider and darker than the latter; the stripes are interrupted by transverse whitish bands, first 3 bands more widely separated than remainder; head rather spatulate, marked off from body by slight constriction, with 8–10 irregularly distributed small epidermal eyes on each side .................... ................................................................... Carinesta tubulanoides Gibson, 1990 Head rounded, clearly demarcated from body; colour pattern consisting of single mid-dorsal and 2 lateroventral white longitudinal stripes or 2 pale brown dorsal stripes, with transverse bands which may be very obvious or somewhat indistinct .......................................................................................4 Head bluntly rounded, not demarcated from body; anteriorly pale olive brown on all sides, soon posteriorly separating into broad dorsal and ventral longitudinal stripes of some colour which, along lateral margins, fade to a whitish or very pale brown hue; ventral stripe about half to two-thirds width of dorsal..................................................Procephalothrix orientalis Gibson, 1990 General colour light brown with 2 white lateroventral stripes which anteriorly extend to rear of head, and single median dorsal white stripe which almost reaches tip of head and here forms cross; with unevenly spaced white transverse bands, commencing about 2 cm behind head, extending throughout body, head with white margins and white band present immediately in front of mouth.............................................. Tubulanus hylbomi sp. nov. General colour brown, paler ventrally, with 2 distinct dorsal pale brown longitudinal stripes, lateral body margins whitish, with indistinct whitish transverse bands..................................Tubulanus longivasculus sp. nov. Without eyes ..................................................................................................6 Bluntly pointed head on either side with distinct row of up to about 20 eyes extending from tip of snout back to brain region; general colour opaque to translucent white, sometimes with very pale pink tinge posteriorly .............. ................................................ Cephalotrichella alba Gibson & Sundberg, 1992 General colour an opaque to translucent white; mouth ventral, indistinct 7 Mouth ventral, large and distinct, located some distance behind anterior tip; colour variable, ranging from an overall pale translucent yellowish in smaller individuals to a general bright orange in large specimens; in smaller examples tip of head often distinctly orange, this colour sometimes extending back into trunk region before fading to yellowish; sexually mature specimens almost entirely orange with gonads appearing as whitish patches along lateral margins .......................................Procephalothrix arenarius Gibson, 1990 (Brain and longitudinal nerve cords situated between epidermal basement layer and body wall outer circular muscle layer) ...........................................................................8 (Brain and longitudinal nerve cords situated in proximal region of epidermis; cerebral sensory organs present; body wall musculature comprising outer circular and inner longitudinal layers, but with inner circular layer present in foregut region; blood system without mid-dorsal vessel)...................................... Carinina sinensis sp. nov. (With cerebral sensory organs; mid-dorsal blood vessel present; body wall musculature comprising outer circular and inner longitudinal layers)............................................9 (Without cerebral sensory organs; mid-dorsal blood vessel absent; body wall musculature
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comprising outer circular, middle longitudinal and inner circular layers)....................10 (Blood system in foregut region with lateral vessels developed into vascular plexus; middorsal blood vessel penetrating rhynchocoel to form rhynchocoelic villus; brain lobes transversely linked by 2 dorsal commissures).............Hubrechtella alba Gibson, 1997 (Blood system in foregut region consisting of two lateral vessels which do not form a vascular plexus; mid-dorsal blood vessel not forming a rhynchocoelic villus; brain lobes transversely linked by 1 dorsal commissure) ................................................................ ............................................................. Hubrechtella sinimarinus sp. nov. (Posterior end of rhynchocoel with massive muscular sac formed from circular muscle fibres; proboscis with complex construction, with several histologicall distinct regions)............... .....................................................................Callinera bergendali sp. nov. (Posterior end of rhynchocoel without muscular sac; proboscis simple, with more or less uniform construction throughout its length)................................................................ ...................................................... Parahubrechtia jillae gen. et sp. nov.
ACKNOWLEDGEMENTS
PS wishes to thank Professor Brian Morton for inviting him to participate in the Fourth International Marine Biological Workshop, held in Hong Kong during April 1989, during which time the palaeonemerteans described in this paper were collected. Financial support for the study, provided to PS by the Swedish Natural Science Research Council, is gratefully acknowledged. Our thanks are also due to Professor ‘Pete’ Riser, Dr Jon Norenburg and Dr Alex Rogers for commenting on the original manuscript.
REFERENCES
¨ ber ein Paar sehr eigenthu¨mliche nordische Nemertinen. Zoologischer Anzeiger Bergendal D. 1900. U 23: 313–328. Bergendal D. 1902. Zur Kenntniss der nordischen Nemertinen. Bergens museums a˚rbog No. 4: 1–22. Bergendal D. 1903. Till ka¨nnedomen om de nordiska Nemertinerna. 4. Fo¨rteckning o¨fver vid Sveriges vestkust iakttagna Nemertiner. Arkiv fo¨r Zoologi 1: 85–156. Bu¨rger O. 1904. Nemertinen. Resultats du voyage du S.Y. Belgica en 1897–1899, Zoologie: 1–10. Coe W.R. 1951. Geographical distribution of the nemerteans of the northern coast of the Gulf of Mexico as compared with those of the southern coast of Florida, with descriptions of three new species. Journal of the Washington Academy of Sciences 41: 328–331. ¨ kologie der Nemertinen der Kieler Friedrich H. 1935a. Studien zur Morphologie, Systematik und O Bucht. Archiv fu¨r Naturgeschichte 4: 293–375. Friedrich H. 1935b. Carinina poseidoni n. sp., eine neue Palaeonemertine aus der Nordsee. Zoologischer Anzeiger 109: 64–72. Friedrich H. 1958. Nemertini. The Zoology of Iceland 2 (Part 18): 1–24. Friedrich H. 1970. Nemertinen aus Chile. Sarsia 40: 1–80. Gibson R. 1979a. Hubrechtella malabarensis sp. nov. (Palaeonemertea: Hubrechtidae), a new nemertean from Australia. Zoologischer Anzeiger 202: 119–131. Gibson R. 1979b. Nemerteans of the Great Barrier Reef. 1. Anopla Palaeonemertea. Zoological Journal of the Linnean Society 65: 305–337. Gibson R. 1990. The macrobenthic nemertean fauna of Hong Kong. In: Morton B, ed. Proceedings of the Second International Marine Biological Workshop: the Marine Flora and Fauna of Hong Kong and Southern China. Vol. 1. Hong Kong: Hong Kong University Press, 33–212. Gibson R. 1994. Nemerteans. Shrewsbury: Field Studies Council.
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Gibson R. 1995. Nemertean genera and species of the world: an annotated checklist of original names and description citations, synonyms, current taxonomic status, habitats and recorded zoogeographic distribution. Journal of Natural History 29: 271–561. Gibson R. 1997. New benthic nemerteans from Hong Kong. In: Morton B, ed. The Marine Flora and Fauna of Hong Kong and Southern China IV Vol. 1, 9–29. Hong Kong: Hong Kong University Press. Gibson R, Sundberg P. 1992. Three new nemerteans from Hong Kong. In: Morton B, ed. The Marine Flora and Fauna of Hong Kong and Southern China III. Vol. 1 Hong Kong: Hong Kong University Press, 97–129. Hubrecht AAW. 1885. The Nemertea. Narrative of the Cruise of H.M.S. Challenger Expedition 1: 830–833. Hubrecht AAW. 1887. Report on the Nemertea collected by H.M.S. Challenger during the years 1873–76. Reports of the Scientific Results of the Voyage of H.M.S. Challenger 1873–76, Zoology 19: 1–150. Hylbom R. 1957. Studies on palaeonemerteans of the Gullmar Fiord area (west coast of Sweden). Arkiv fo¨r Zoologi, Series 2 10: 539–582. Iwata F. 1957. Nemerteans from Sagami Bay. Publications from the Akkeshi Marine Biological Station 7: 1–31. Iwata F. 1960. Studies on the comparative embryology of nemerteans with special reference to their interrelationships. Publications from the Akkeshi Marine Biological Station 10: 1–51. Joubin L. 1902. Ne´mertiens. Expe´ditions scientifiques du ‘Travailleur’ et du ‘Talisman’ 4: 181–220. Kirsteuer E. 1967. New marine nemerteans from Nossi Be, Madagascar. Zoologischer Anzeiger 178: 110–122. Korotkevich VS. 1982. Novuie i redkie vidui nemertin (Nemertini) s yuzhnogo shelfa ostrova sakhalin. Issledovaniya Faunui Morei 37: 12–26. Kulikova VI. 1984. Novyi vid nemertiny roda Carinina (Palaeonemertini, Tubulanidae) iz belogo morya. Zoologicheskii zhurnal 63: 1092–1095. Mu¨ller GJ. 1965. Carinina heterosoma n. sp. si cıˆteva consideratii asupra genului Carinina (Vermes, Palaeonemertini). Hidrobiologia 6: 243–257. Nawitzki W. 1931. Procarinina remanei. Eine neue Pala¨onemertine der Kieler Fo¨rde. Zoologische Jahrbu¨cher, Abteilungen Anatomie and Ontogenie der Tiere 54: 159–234. Renier SA. 1804. Prospetto della classe dei Vermi. An uncompleted work issued in 1804 (see G. Meneghini, 1847, [ed.] Osservazioni postume di zoologia Adriatica del Professore Stefano Andrea Renier, Venezia: Giovanni Cecchini, XV-XXVII). Rogers AD, Gibson R, Thorpe JP. 1992. A new species of Callinera (Nemertea, Anopla, Palaeonemertea) from the Isle of Man. Zoologica Scripta 21: 119–128. Sundberg P, Erse´us C, Mackie ASY. 1992. Distribution of annelids and nemerteans along three transects at Hoi Ha beach. In: Morton B, ed. The Marine Flora and Fauna of Hong Kong and Southern China III. Vol. 2. Hong Kong: Hong Kong University Press, 865–881. Sundberg P, Hylbom R. 1994. Phylogeny of the nemertean subclass Palaeonemertea (Anopla, Nemertea). Cladistics 10: 347–402. Taylor JD. 1992. Long-term changes in the gastropod fauna of Tolo Channel and Mirs Bay, Hong Kong: the 1989 survey. In: Morton B, ed. The Marine Flora and Fauna of Hong Kong and Southern China III. Vol. 2. Hong Kong: Hong Kong University Press, 557–575. Wheeler JFG. 1940. Nemerteans of Kerguelen and the southern ocean. Report, B.A.N.Z. Antarctic Research Expedition 1929–31, Series B 4: 233–256.
Six new species of palaeonemerteans (Nemertea) from Hong Kong RAY GIBSON FLS∗ School of Biological and Earth Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF PER SUNDBERG Department of Zoology, Go¨teborg University, Medicinaregatan 18, S-400 31 Go¨teborg, Sweden Received February 1997; accepted for publication September 1997
One new genus and six new species of palaeonemerteans are described and illustrated from Hong Kong and the New Territories; these are Hubrechtella sinimarinus sp. nov. and Parahubrechtia jillae gen. et sp. nov. in the Hubrechtidae, and Callinera bergendali sp. nov., Carinina sinensis sp. nov., Tubulanus hylbomi sp. nov. and Tubulanus longivasculus sp. nov. in the Tubulanidae. These bring the known number of palaeonemertean species from Hong Kong to 11; a key to these species, based primarily upon features distinguishable in the living animals, is provided. 1999 The Linnean Society of London
ADDITIONAL KEY WORDS:—Taxonomy – morphology – Callinera – Carinina – Hubrechtella – Parahubrechtia gen. nov. – Tubulanus. CONTENTS
Introduction . . . . . . . . . . Material and methods . . . . . . Abbreviations . . . . . . . . . Observations . . . . . . . . . Family Hubrechtidae . . . . . Genus Hubrechtella Bergendal, 1902 . Hubrechtella sinimarinus sp. nov. Genus Parahubrechtia gen. nov. . . Parahubrechtia jillae sp. nov. . Family Tubulanidae . . . . . Genus Callinera Bergendal, 1900 . . Callinera bergendali sp. nov. . . Genus Carinina Hubrecht, 1885 . . Carinina sinensis sp. nov. . . . Genus Tubulanus Renier, 1804 . .
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Tubulanus hylbomi sp. nov. . . . Tubulanus longivasculus sp. nov. . Key to the palaeonemerteans of Hong Kong Acknowledgements . . . . . . . . References . . . . . . . . . . .
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INTRODUCTION
Several new species of nemerteans have recently been described from Hong Kong (Gibson, 1990, 1997; Gibson & Sundberg, 1992); among these, five are included in the two anoplan orders Archi- or Palaeonemertea. The taxon Archinemertea was originally proposed by Iwata (1960) to contain three genera, Cephalotrichella, Cephalothrix and Procephalothrix, which were previously included with the Palaeonemertea in the family Cephalothricidae. However, Sundberg & Hylbom (1994), using cladistic analyses to assess the phylogeny of the archi- and palaeonemerteans, concluded that their separation could no longer be supported. Although the cephalothricid genera form a monophyletic group within the clade Palaeonemertea, the retention of the Archinemertea as a distinct order would make the Palaeonemertea paraphyletic and Sundberg & Hylbom (1994) accordingly rejected the name Archinemertea. Based upon their arguments, five species of palaeonemerteans have thus been recorded from Hong Kong; these are Carinesta tubulanoides Gibson, 1990, Cephalotrichella alba Gibson & Sundberg, 1992, Hubrechtella alba Gibson, 1997, Procephalothrix arenarius Gibson, 1990, and Procephalothrix orientalis Gibson, 1990. During a visit to Hong Kong in 1989, six further species of palaeonemerteans were discovered by PS. The principal anatomical features of these species were included in the phylogenetic analyses of Sundberg & Hylbom (1994), under the reference numbers HK sp. 1 to HK sp. 6 inclusive, but in the present paper they are named and fully described for the first time.
MATERIAL AND METHODS
The nemerteans were collected during 1989 from sampling sites off the New Territories, Hong Kong (Fig. 1). Specimens were anaesthetized in either 7.5% MgCl2 or MS222, examined for external features and then fixed in seawater Bouin’s solution, sectioned at 7 lm in 58°C m.p. paraffin wax and stained by the Mallory trichrome method. Type material is deposited in the Stockholm Museum of Natural History (SMNH).
ABBREVIATIONS
BC BE BN CC CD
buccal nerve commissure buccal epithelium buccal nerve ciliated cerebral canal cephalic glands
CG CL CM CN CO
cerebral ganglia cephalic lacuna body wall circular muscle layer cephalic neural layer cerebral sensory organ
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CV DC DG DL DN DV EB EP EX FG FN FV GO IC IN LD LF
cerebral organ blood vessel dorsal cerebral commissure dorsal cerebral ganglion dorsolateral blood lacuna dorsal nerve mid-dorsal blood vessel epidermal basement layer epidermis excretory tubule foregut foregut nerve branch of foregut vascular plexus gonad body wall inner circular muscle layer intestine lower dorsal nerve longitudinal muscles between cerebral ganglia and epidermal basement layer
LM LN LO LP LV MS MT OC PI PN PR RB RC RD RM VB VC VG
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body wall longitudinal muscle layer lateral nerve cord lateral sensory organ longitudinal muscle plate lateral blood vessel posterior muscle sac of rhynchocoel mouth body wall outer circular muscle layer proboscis insertion proboscis nerve proboscis rhynchocoel body rhynchocoel rhynchodaeum proboscis retractor muscle blood vessel leading to rhynchocoel body ventral cerebral commissure ventral cerebral ganglion
OBSERVATIONS
Family Hubrechtidae Genus Hubrechtella Bergendal, 1902 Diagnosis. Gibson (1979a) defines the genus as palaeonemerteans with two body wall muscle layers consisting of outer circular and inner longitudinal fibres; brain and lateral nerve cords situated between epidermal ‘neural’ connective tissue layer (anteriorly) or epidermal basement membrane (posteriorly) and circular musculature of body wall; nervous system with a single pair of giant fibres extending through the brain lobes and lateral nerve cords; proboscis with two (outer longitudinal, inner circular) or three (outer and inner circular, middle longitudinal) muscle layers; rhynchocoel not fully body length; blood system with three main post-cerebral channels consisting of unpaired mid-dorsal and paired lateral vessels; no excretory system; no eyes; cerebral sensory organs well developed, positioned at rear of brain and enclosed by lateral blood vessels; sexes separate.
Hubrechtella sinimarinus sp. nov. (Figs 2–4) HK sp. 3 in Sundberg & Hylbom (1994) Type specimen. Holotype: immature female, series of transverse sections through the anterior and intestinal regions of the body (8 slides), SMNH 4889.
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Figure 1. Map of part of the New Territories, Hong Kong, to show the location of collecting sites referred to in the text. 1, Hoi Ha Wan; 2, Trawl 13; 3, Trawl 51; 4, Flat Island.
Type locality. Hoi Ha Wan (Location 1, Fig. 1), south-west of Flynn Point, from mussel beds on shell sand at 7 m depth. Etymology. The specific epithet, denoting that the species was found in the China Sea, is a composite between the Latin Sinae (an Oriental people mentioned by Ptolemy, now the Chinese) and marinus (of the sea). External features. The nemerteans were up to 15 mm long with slender bodies, 0.3 mm wide anteriorly, 0.5 mm posteriorly (Fig. 2). The spatulate head was clearly demarcated from the remainder of the body and had neither eyes nor cephalic furrows. The ventral mouth was visible about 1.5 mm behind the anterior tip. The general colour was an opaque white, although intestinal contents sometimes imparted a brownish tinge posteriorly.
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Figure 2. Hubrechtella sinimarinus sp. nov. A, drawing of complete specimen to show the general appearance of the body. B, enlargement to show the shape of the head. Scale bar applies to (A) only.
Body wall, musculature and parenchyma. As in other Hubrechtella species, the epidermis is better developed anteriorly. On the head it is up to 45 lm thick, decreasing posteriorly to a maximum of 30 lm or less in the intestinal regions. Unfortunately the epidermis has sloughed off from several parts of the body, so a detailed comparison between the distribution of the various gland cell types, described by Hylbom (1957) for the type species, Hubrechtella dubia Bergendal, 1902, cannot be made. Beneath the epidermis the basement membrane is distinct but thin, rarely more than 2–3 lm. In the head the nervous layer reported between the epidermal basement membrane and body wall circular muscle layer in some species (Hylbom, 1957; Gibson, 1979a, b), is also evident and can be traced back into the foregut region of the body, where it is 5–8 lm thick. The body wall muscle layers are typical for the genus. The circular layer is about 6–8 lm in maximum thickness throughout most of the body length, although tending to be less posteriorly, whereas the longitudinal muscles are 15–30 lm deep in the foregut region but up to 60 lm in the intestinal region. The so-called zigzag fibres reported in the longitudinal muscle layer of Hubrechtella dubia, Hubrechtella malabarensis Gibson, 1979, and Hubrechtella alba Gibson, 1997 (Hylbom, 1957; Gibson, 1979a; 1997), are also distinguishable in the present form (Fig. 3), although they are missing from other members of the genus (Kirsteuer, 1967; Gibson, 1979b). Parenchymatous connective tissues are nowhere strongly developed. Proboscis apparatus. The tip of the head, in front of the proboscis insertion, was unfortunately lost during sectioning; no observations can thus be made about the rhynchodaeum. The rhynchocoel is shorter than the body, extending about 65–70% of the body length; its wall contains separate circular and longitudinal muscle layers which are each mostly 4–6 lm thick, although in the foregut region the circular layer is better developed (Fig. 3). The proboscis insertion is presumed to be pre-cerebral, as in other members of the genus. In the retracted position the proboscis is about 165 lm in overall diameter and consists of an outer and richly glandular epithelium, up to about 60 lm thick, an outer circular muscle layer at most only two or three fibres thick, an inner
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Figure 3. Hubrechtella sinimarinus sp. nov. Camera lucida drawing of transverse section through the foregut region to show the organisation of various body structures. Note the zigzag arrangement of the muscle fibres in the proximal regions of the body wall longitudinal musculature.
longitudinal muscle coat 10–15 lm across and a thin but distinct inner lining (Fig. 4). The proboscis morphology is similar throughout the length of the organ. No proboscis nerves could be distinguished. The proboscis retractor muscle is well developed (Fig. 3). Alimentary canal. The slit-like mouth opens close behind the brain. The buccal wall, 60–70 lm or more thick, is richly glandular and densely ciliated. Two major types of gland cells are distinguishable, both containing coarsely granular secretions. Basophilic glands occur on all margins of the foregut, but the acidophils are mainly restricted to the dorsal and lateral margins. A delicate layer of circular muscles, at most only a few fibres thick and not evident in all parts of the foregut, surrounds the foregut, whilst a thin layer of longitudinal muscles dorsally extends between the foregut and rhynchocoel walls (Fig. 3); in several places isolated longitudinal muscle fibres can also be seen alongside and ventrolaterally to the foregut wall. The intestinal wall is up to 60 lm or more thick and contains only acidophilic glands. There are no lateral diverticula. Blood system. The arrangement of the cephalic blood supply is not known. In the cerebral ring a pair of rather compressed lateral lacunae extend back, one on either side of the rhynchocoel. These begin to enlarge as the dorsal and ventral brain lobes separate posteriorly and, anterior to the mouth, are penetrated by the cerebral sensory organs (Fig. 4). Unlike the condition in Hubrechtella alba (Gibson, 1997) the two vessels do not fuse ventrally behind the ventral cerebral commissure. A middorsal vessel extends below the rhynchocoel (Fig. 3) but no evidence of a rhynchocoelic villus, as found in some hubrechtids, could be distinguished. This condition is similar
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Figure 4. Hubrechtella sinimarinus sp. nov. Camera lucida drawing of oblique section through the cerebral region to show a ciliated cerebral canal, cerebral sensory organ, the anterior portion of the proboscis and the general arrangement of this part of the body.
to that described for Hubrechtella indica Kirsteuer (1967) and Hubrechtella queenslandica (Gibson, 1979b), which also have no rhynchocoelic villus. In the foregut region the two vessels do not form a vascular plexus, remaining separate throughout the length of the body in a lateral or ventrolateral position (Fig. 3). Several members of the genus are known to possess a foregut vascular plexus, formed by subdivision of the two lacunae, but none is found in Hubrechtella indica or Hubrechtella sarodravayensis (Kirsteuer, 1967). There is no evidence of pseudometameric transverse connectives between the blood channels in the intestinal region and none have been recorded for any other member of the genus. Nervous system. The brain lobes and lateral nerve cords are situated between the epidermal basement membrane and the body wall circular muscle layer. The brain lobes are well developed, the dorsal rather larger than the ventral. The slender dorsal cerebral commissure, 4–5 lm thick, is located posterior to the ventral commissure, which is 20–25 lm wide. Hubrechtella alba from Hong Kong, unlike the present form, is the only member of the genus known to possess two dorsal commissures (Gibson, 1997). The lateral nerves lead from the rear of the ventral ganglia; the giant nerve fibre, described in the lateral nerves for several Hubrechtella species, could not be distinguished in the present form. The fibrous core of each dorsal brain lobe is forked posteriorly into outer dorsal and inner ventral branches, the latter innervating the cerebral sensory organs (Fig. 4). This condition closely resembles that described for other members of the genus. Both upper and lower median dorsal nerves can be followed from the rear of the
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dorsal commissure back into the foregut region. The upper nerve runs between the epidermal basement layer and the body wall circular muscles, the lower in the longitudinal muscle layer. From the rear of the ventral commissure a single median nerve leads back towards the mouth; this nerve, evidently leading to the foregut neural supply, forks a short distance in front of the mouth but could not be traced further (Fig. 4). Sense organs. As in other species of Hubrechtella, there are neither eyes nor lateral sensory organs. The cerebral sensory organs are large and well developed (Fig. 4). Towards the rear of the brain the lateral epidermis forms a short, shallow indentation lined by long (15 lm) cilia and entirely lacking gland cells. At the rear of the indentation on each side of the body a ciliated cerebral canal, 20 lm in diameter, leads directly inwards in a medioventral direction to a cerebral organ (Fig. 4). The cerebral canals enter the blood vessels in the brain region, enter the cerebral organs which are composed of a complex of glandular and neuroganglionic cells below the cerebral organ nerve, and then extend towards the rear of the organs close to their outer lateral surface. The cerebral organs are contained entirely within the lumen of each lateral blood lacuna except where their ciliated canals enter them anteriorly. Each organ is ovoid, about 50–55 lm wide, 90 lm in dorsoventral extent and 110 lm long; the organs reach back to the oral region. Excretory system. As in other species of Hubrechtella (Hylbom, 1957; Kirsteuer, 1967; Gibson, 1979a, b, 1997), no evidence of an excretory system has been found. Reproductive system. The single specimen is an immature female. The ovaries are packed close together in the intestinal region, forming ‘blocks’ of reproductive organs extending along the lateral and dorsolateral margins of the body. Systematic discussion. Nine species of Hubrechtella have been described previously (Gibson, 1995, 1997), all sharing many anatomical features. Sundberg & Hylbom’s (1994) phylogeny of the palaeonemerteans shows that the present form belongs in a clade along with four of these, including the type species for the genus Hubrechtella dubia. The arrangement of the body wall layers, well developed cerebral sensory organs intimately associated with the blood system, position of the central nervous system in relation to the body wall and absence of an excretory system, enable the present taxon to be placed in the genus. Among the previously known hubrechtellids two species have been recorded from Madagascar (Kirsteuer, 1967), two from Australia (Gibson, 1979a, b) and one (Hubrechtella alba) from Hong Kong (Gibson, 1997); the remaining four are known only from European waters (Gibson, 1995). Hubrechtella alba differs from the present form in its relatively much smaller-sized proboscis, possession of two dorsal cerebral commissures, organization of its anterior blood supply into a foregut vascular plexus, and in having a mid-dorsal blood vessel within a rhynchocoelic villus (Gibson, 1997). The Indo-Pacific forms differ from the present species in the following ways: Hubrechtella queenslandica possesses a proboscis with three muscle layers and no zigzag fibres in its body wall longitudinal musculature (Gibson, 1979b), and the three other taxa (H. indica, H. malabarensis and H. sarodravayensis) do not possess a circular muscle layer around their foreguts (Kirsteuer, 1967; Gibson, 1979a), and H. sarodravayensis and H. indica have no zigzag fibres in their longitudinal muscle layers. The present form cannot therefore be identified as belonging to any of the previously known
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species of Hubrechtella and it is accordingly described as a new species, for which the name Hubrechtella sinimarinus is proposed.
Genus Parahubrechtia gen. nov. Diagnosis. The genus Parahubrechtia gen. nov. may be defined as palaeonemerteans that lack head furrows; body wall musculature comprising outer and inner circular and middle longitudinal layers; muscle crosses between body wall circular layers missing; without cerebral sensory organs; lateral organs present; cephalic region with nerve layer; proboscis with outer circular and inner longitudinal muscle layers; proboscis nerves present; brain and lateral nerve cords situated between epidermal basement membrane and body wall outer circular muscles; nervous system with neither neurochords nor neurochord cells; buccal nerves paired; intestine without lateral diverticula; rhynchocoel wall primarily with circular musculature but isolated longitudinal fibres also present; excretory system simple, anteriorly penetrating lateral blood vessels; blood vascular system simple, without mid-dorsal vessel; eyes absent; sexes probably separate; with neither frontal glands nor apical organ. Etymology. The generic name, indicating its affiliation with the family Hubrechtidae, is formed from the Greek prefix para (near or alongside) and the name of the type genus for the family, Hubrechtia. Type species. Parahubrechtia jillae sp. nov.
Parahubrechtia jillae sp. nov. (Figs 5–8) HK sp. 2 in Sundberg & Hylbom (1994) Type specimens. Holotype: female, complete set of transverse sections (4 slides), paratype: female, complete set of transverse sections (4 slides), SMNH 4890. Type locality. Hoi Ha Wan (Location 1, Fig. 1), southwest of Flynn Point, collected from 7 m depth on shell sand. Etymology. The species is named after Jill Gibson, the first author’s wife, who has unfailingly supported his research interest in nemerteans. External features. The nemerteans were 6–10 mm long but only about 0.3 mm wide. The body was rather flattened dorsoventrally, the spatulate head distinct in life (Fig.
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Figure 5. Parahubrechtia jillae gen. et sp. nov. Drawing to show the general appearance of a living specimen.
Figure 6. Parahubrechtia jillae gen. et sp. nov. Camera lucida drawing of transverse section through the cephalic region.
5). The intestine was clearly visible through the whitish, translucent, posterior half of the body, the pointed posterior tip looking distinctly fragile. The body exhibited a distinct thickening and the epidermis was milky white and papillose, about onethird back from the anterior end. Body wall, musculature and parenchyma. The epidermis in the cephalic region is 30–40 lm tall, internally lined by a thin but distinct connective tissue membrane (Fig. 6).
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Figure 7. Parahubrechtia jillae gen. et sp. nov. Camera lucida drawing of transverse section through the anterior intestinal region close to the lateral sensory organs.
Behind the brain the epidermal height is reduced to about 20–30 lm, a further reduction occurring throughout the intestinal region where the epidermis is often only 15 lm or less thick. Gland cells of various types are distributed throughout the length of the body, but close in front of the brain a zone of loosely distributed Orange G positive glands, containing coarsely granular cytoplasm, forms a distinct layer in the distal third of the epidermis. In the intestinal region, just in front of the nephridiopores and lateral sensory organs, a band of densely packed and strongly acidophilic glands, filling the proximal half of the epidermis, encircles the body. This region extends back for 100–120 lm before suddenly disappearing; similar glands are not found elsewhere in the epidermis. The body wall musculature comprises outer circular, middle longitudinal and inner circular layers which, in the foregut region, are respectively some 3–6 lm, 15–25 lm and 2–3 lm thick. In the brain region the outer circular muscles are reduced in thickness, but the longitudinal layer is up to 35–40 lm deep. Precerebrally isolated dorsoventral muscle fibres cross the head between the various cephalic structures. The inner circular layer is missing from the cephalic and cerebral regions but extends for a short distance into the intestinal part of the body (Fig. 7). Between the rhynchocoel and foregut wall a loosely arranged layer of longitudinal muscles, mostly only a single fibre thick, extends back into the intestinal region (Fig. 7) almost as far as the posterior end of the rhynchocoel. There are no intrinsic muscles associated with any part of the gut, and dorsoventral muscle bundles are absent from the intestinal region. The outer circular and longitudinal muscle layers are not as well developed in the posterior half of the body. Parenchymatous connective tissues are poorly developed.
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Figure 8. Parahubrechtia jillae gen. et sp. nov. Camera lucida drawing of transverse section through the brain region just behind the ventral cerebral commissure.
Proboscis apparatus. The proboscis pore is subterminal and ventral; it opens about 60–70 lm behind the tip of the head. It leads into a rhynchodaeum whose epithelium, 5–15 lm thick, is neither ciliated nor glandular (Fig. 6). The proboscis insertion is situated between the brain lobes. The two proboscis nerve roots, which emerge from the dorsal margins of the ventral ganglionic lobes, enter the proboscis insertion ventrolaterally. The rhynchocoel, about half the body width in diameter, extends for about 60% of the body length. Its wall is composed principally of a circular muscle layer, 5–6 lm thick, but isolated longitudinal muscle fibres, which do not form a definite layer, extend between the circular muscles and the innermost body wall musculature (Fig. 7). The proboscis (Figs 6–8) is slender, about 70–80 lm in diameter when retracted. It has a more or less uniform construction throughout its length, comprising a glandular epithelium 12–20 lm tall, an outer circular muscle layer 2–3 lm across, an inner longitudinal muscle coat 3–6 lm thick, and a thin inner lining. The two proboscis nerves are situated on opposite sides of the organ between the epithelium and circular muscle layer (Fig. 8); each nerve is 6–8 lm in diameter. Below each nerve, but separated from it by the circular muscles, a ‘strand’ of Orange G positive tissue extends the full proboscis length; the significance of these tissues is not known. The thick retractor muscle is attached to the dorsal rhynchocoel wall near its posterior end. Alimentary canal. The ventral mouth is situated immediately behind the brain. The buccal epithelium is 10–20 lm thick, glandular and ciliated. Throughout the foregut the epithelium is little folded and thinner than that of the buccal region. The intestinal epithelium, up to 30 lm thick, has a typical palaeonemertean appearance. There are no lateral diverticula, both the intestine (Fig. 7) and foregut
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essentially forming a simple tubular canal arching below the rhynchocoel. Behind the rhynchocoel the intestine occupies most of the body space between the lateral rows of gonads. Blood system. The simple blood system (Figs 6–8) is similar to that described for cephalothricid palaeonemerteans. It consists of a single pair of thin-walled, spacious lateral vessels, joined anteriorly by a cephalic loop in front of the proboscis pore and posteriorly by a transverse supra-intestinal connective. There is no mid-dorsal vessel and no other transverse connectives. In the foregut and anterior intestinal regions the lateral vessels run internal to the body wall inner circular muscles, but close in front of the lateral sensory organs the vessels pass through this layer and continue posteriorly between it and the body wall longitudinal musculature (Fig. 7). Behind the posterior limit of the inner circular muscles the vessels continue just internal to the longitudinal layer. Nervous system. The brain, situated between the epidermal basement layer and body wall outer circular musculature, is comparatively large and well developed. The dorsal lobes are larger than, and extend in front of, the ventral. Longitudinal muscle bundles between the brain and epidermis, as described later for the two Tubulanus species, are missing. The dorsal lobes are more lateral in position than the ventral lobes (Fig. 8). Dorsal and ventral cerebral commissures are at about the same level, the former 12–15 lm thick, the latter 20–22 lm. Neither an inner nor outer neurilemma can be distinguished, nor are there any neurochord cells. The longitudinal nerves lead from the rear of the ventral ganglia and extend the full length of the body in a lateral position (Fig. 7). The peripheral nervous system is also well developed. In the head a distinct neural layer, up to 8–10 lm thick, is present between the epidermal basement layer and the body wall outer circular musculature (Fig. 6). Several distinct nerve tracts are evident in the layer, which originates from the anterior margins of both dorsal and ventral ganglionic lobes. A median dorsal nerve, 12 lm thick, extends backwards immediately below the epidermal basement layer; a lower dorsal nerve, situated internal to the outer circular musculature (Fig. 7), is distinguishable only in the anterior intestinal region. The proboscis nerves lead from the dorsal surface of the ventral brain lobes, and close behind these a single nerve emerges from the inner ventrolateral border of each ventral lobe, curving upwards and inwards to a thick (20 lm or more) transverse commissure located close in front of the mouth just below the rhynchocoel (Fig. 8). The two buccal nerves, 15 lm in diameter, lead from the rear of this commissure, lead back on either side of the mouth and can be followed for only a short distance adjacent to the foregut wall. Sensory organs. The present species possesses neither eyes nor cerebral sensory organs. What are interpreted as simple lateral epidermal sensory organs are present, however, just in front of the nephridiopores. Level with the dorsal margins of the lateral nerves a simple pit on each side of the body (Fig. 7) leads to an intraepidermal chamber, some 15 lm in diameter, which ends close to the lateral nerves. The epidermal tissues adjacent to these pits, which are lined by long dense cilia, lack the gland cells which occur elsewhere at this level. Frontal glands and apical organ. Neither an apical organ nor frontal glands are present in this species.
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Figure 9. Callinera bergendali sp. nov. Drawing to show the general appearance of a living specimen.
Excretory system. The excretory system, extending for approximately 150 lm, opens just behind the dense band of acidophilic epidermal gland cells. A single large collecting tubule on each side lies immediately above each lateral blood vessel, outside the body wall inner circular muscle layer (Fig. 7). The tubules are thickwalled (10–12 lm) for most of their length, but are anteriorly thinner-walled where they lie adjacent to the outer lateral margins of the vessels and bulge into each vessel lumen. Small amounts of Orange G positive material are associated with the intravascular inpushings, but whether these represent glandular terminal organs, as described for some palaeonemertean species, could not be determined. Posteriorly the collecting tubules end in slender efferent ducts which open via a single dorsolateral nephridiopore on each side of the body. Reproductive system. The sexes, as in other hubrechtid species, are probably separate. Both specimens obtained are female, the ovaries lying in a densely distributed lateral row on either side of the body, commencing just before the end of the rhynchocoel. Ova in several stages of development are distinguishable within each individual, larger eggs containing a single ovoid nucleus about 40 lm in diameter in which a single distinct nucleolus, 7–8 lm across, is positioned excentrically. Systematic discussion. This species makes a clade in Sundberg & Hylbom (1994: Fig. 9) with Hubrechtella dubia, H. malabarensis, H. queenslandica, H. sarodravayensis, Tetramys ramicerebrum Iwata, 1957, Tubulanus lucidus Iwata, 1957, and HK sp. 3, thus supporting Hylbom’s (1957) suggestion that Tubulanus lucidus should also be included in the genus Hubrechtella. According to the traditional classification of nemertean families and genera, both Hubrechtella and Tetramys belong in the Hubrechtidae, which also includes two other genera, Coeia and Hubrechtia. Sundberg & Hylbom’s (1994: Table 4) matrix of characters used to define the various palaeonemertean genera shows that Hubrechtella and Tetramys share several anatomical features, including length at the onset of sexual maturity, absence of eyes, presence of a neural layer rather than separate cephalic nerves, position of the cerebral ganglia and lateral nerve cords, presence of paired buccal nerves, and occurrence of a single mid-dorsal blood vessel that enters the rhynchocoel wall. Most Hubrechtella species also resemble Tetramys in lacking a horizontal muscle plate between the rhynchocoel and alimentary canal and in lacking lateral sensory organs. Hubrechtella queenslandica resembles Tetramys in possessing three proboscis muscle layers, whereas all other Hubrechtella species known have only two. The present taxon differs from both these genera in lacking a mid-dorsal blood vessel but possessing a horizontal muscle plate between the rhynchocoel and foregut,
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and in being much smaller at the onset of sexual maturation. It also differs from Tetramys in possessing two, rather than three, proboscis muscle layers. Hubrechtia, the type genus for the family Hubrechtidae, differs from the Hong Kong form in possessing cerebral sensory organs, which are also found in Hubrechtella and Tetramys, and in having two nerves in its rhynchodaeal epithelium, a median dorsal blood vessel and intestinal diverticula, whilst Coeia has cerebral but no lateral sensory organs, no proboscis nerves, intestinal diverticula, a mid-dorsal blood vessel and a rhynchocoel wall with an inner longitudinal muscle layer. It is accordingly concluded that the present form, whilst being closely related to these hubrechtid genera according to the analyses of Sundberg & Hylbom (1994), is sufficiently different to warrant separate generic status and it is therefore named Parahubrechtia jillae gen. et sp. nov. Family Tubulanidae Genus Callinera Bergendal, 1900 Diagnosis. Hylbom (1957: 552) gave the following diagnosis for the genus Callinera: “Nervous system situated between the basement membrane and the outer circular muscle layer. No cerebral sense organs. In the posterior end of the proboscis sheath a peculiar, well-developed muscle sac. Basement membrane thin.” Callinera bergendali sp. nov. (Figs 9–12) Callinera sp. in Sundberg et al. (1992), HK sp. 4 in Sundberg & Hylbom (1994) Type specimens. Holotype: immature, complete set of transverse sections (5 slides), paratypes: four sets of 4 slides each, transverse sections of immature specimens, SMNH 4891. Type locality. Hoi Ha Wan (Location 1, Fig. 1), north of Joss House Point, 7 m depth in heterogeneous shell sand. Other locations. Hoi Ha Wan, Station B6, lower shore intertidal, coarse sand with H2S near the surface (see Sundberg et al., 1992). Etymology. The species is named in honour of the Swedish zoologist, Professor David Bergendal, who studied Scandinavian nemerteans around the turn of the present century and established the genus Callinera. External features. The specimens found were up to 8 mm long and 0.3 mm wide. The body tapered at both ends (Fig. 9). They were whitish, somewhat opaque, with the anterior half of the body more transparent than the milky posterior region. Eyes, cephalic furrows and mouth were indistinguishable in life. Body wall, musculature and parenchyma. The cephalic epidermis is 30–45 lm tall; in its most anterior regions there is no obvious basement membrane, this beginning to appear commensurate with the anterior limits of the cephalic nerves and is then distinct throughout the remaining length of the body. In the cephalic region two
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principal types of epidermal secretory cells are distinguishable; dorsally the glands are large, somewhat vacuolate, irregular in shape and have no particular staining affinities, whereas ventrally the glands are smaller, basophilic and contain a coarsely granular cytoplasm. In the brain region the epidermis laterally is often only about 10 lm thick and contains few secretory cells, but dorsally and ventrally has a similar height to the more anterior portions of the head. Vacuolate glands are both more abundant in the oral region and extend to most sides of the body. A short distance behind the mouth the glandular components of the epidermis change abruptly. Vacuolate cells almost disappear, to be replaced by strongly acidophilic rhabditoid glands and the granular basophils. These two glandular types together occupy the proximal half of the epidermis. This epidermal region extends posteriorly for some 350 lm before ending as abruptly as it started. For the remaining length of the body the basophilic glands are the most abundant, interspersed with occasional vacuolate cells. In the posterior body regions the epidermis is reduced to a height of 20 lm or less. The epidermal basement membrane is 2–3 lm thick in the oral and foregut regions, but only 1–1.5 lm further back. Connective tissue fibrillae lead from the distal surface of the basement layer into the proximal portions of the epidermis, but there is no inner meshwork layer as, for example, in some Tubulanus species. The body wall musculature comprises outer circular, middle longitudinal and inner circular layers, respectively some 3 lm, 30 lm and 1–2 lm thick in the foregut region of the body (Fig. 10). The inner circular layer does not extend into the head, anteriorly ending in the cerebral region, whereas posteriorly it reaches to the hind end of the body although it is often reduced to a single fibre’s thickness and is difficult to distinguish. There are no muscle crosses between the two circular muscle layers, and no dorsoventral muscles in the intestinal region. Commencing just behind the mouth an extremely thin longitudinal muscle plate extends between the rhynchocoel and gut wall; this continues into the intestinal region but terminates in front of the rhynchocoel muscular sac. Cellular parenchyma is not extensive but is evident in the dorsolateral parts of the foregut region (Fig. 10). Proboscis apparatus. The proboscis pore is subterminal. It leads into a tubular rhynchodaeum some 45 lm in overall diameter, whose unciliated epithelium is arranged into four longitudinal blocks of tissue, each about 15–20 lm in maximum width. This condition closely resembles that described for Callinera buergeri Bergendal, 1900. The rhynchodaeum is enclosed by a thin but distinct connective tissue layer, from which fibrils emerge irregularly to lead dorsally or ventrally between the longitudinal muscle fibres. Behind the brain the quadrate arrangement of the rhynchodaeal epithelium tends to become less obvious and the epithelium contains large and irregularly-shaped gland cells, with finely fibrillar cytoplasm, which appear the same as the lightly basophilic cephalic glands of other nemerteans. Towards its posterior end, immediately in front of the proboscis insertion, the rhynchodaeum narrows to form a short tubular region, 15–18 lm in diameter, that is enclosed by a loosely disposed layer of circular muscle fibres. The proboscis insertion is behind the brain, above where the mouth opens into the foregut. The rhynchocoel is approximately 20–25% of the body length and posteriorly ends in a well developed muscle sac (Fig. 11). For most of its length the rhynchocoel forms a spacious but thin-walled chamber, between 40–60% of the body width and
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Figure 10. Callinera bergendali sp. nov. Camera lucida drawing of transverse section through the posterior foregut region to show the arrangement of the various body structures.
lined by a delicate layer of circular muscles, about 2 lm in maximum thickness, and a thin lining epithelium. Towards its posterior end, however, it narrows sharply to form a dorsal tubular canal, only about 40 lm in diameter (i.e. < 10% of the body width) lined by an epithelium that is up to 15 lm thick ventrally. This slender canal ends in a muscular sac formed on the ventral wall of the rhynchocoel; the lumen of the rhynchocoel in this region appears as a narrow and dorsoventrally compressed tube. A posterior rhynchocoel muscle sac or bulb is found in all the Callinera species known, but is not recorded from any other palaeonemertean taxon. The proboscis is extremely slender, at most 60–65 lm in diameter when retracted. It nevertheless possesses a complex construction, with several histologically distinct regions recognisable. The most anterior portion, extending back from the proboscis insertion, is about 500 lm long and consists of a thin outer epithelium with no evident gland cells, an outer longitudinal musculature organised into four distinct blocks of fibres, an extremely thin connective tissue layer and a flattened inner lining. Two small proboscis nerves are evident on opposite sides of the organ between the outer epithelium and the longitudinal musculature. Towards the rear of this region the arrangement of the longitudinal musculature into four blocks becomes less distinct and, just before this region merges into the second part of the proboscis, the longitudinal muscle fibres form a single complete layer. In the second region
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Figure 11. Callinera bergendali sp. nov. Camera lucida drawing of transverse section through the posterior muscle sac of the rhynchocoel.
the epithelium, 8–10 lm thick, is arranged so that opposing sides form a wide Vshape appearing like a double chevron in transverse sections (Fig. 10). One side of this ‘chevron’ contains many Orange G positive glands, but the other has a mostly striated appearance with few glands. The longitudinal musculature of this region is restricted mainly to that side of the proboscis with a glandular epithelium. No nerves could be distinguished in this, or any subsequent, parts of the proboscis. In the third region the epithelium is asymmetrically developed; on one side it is 15–20 lm thick and dominated by large, lightly basophilic gland cells with finely particulate cytoplasm, on the other side the epithelium is almost indistinguishable. The fourth and most posterior portion of the proboscis, terminating in the longitudinal retractor muscle, contains an outer epithelium in which coarsely granular Orange G positive glands predominate and the remaining layers of the organ are almost non-existant. The proboscis retractor muscle leads to the dorsal rhynchocoel wall in front of the posterior muscle sac. Alimentary canal. The small, slit-like mouth opens either below the rear of the brain or immediately behind it, depending upon the degree of contraction of the individual. The foregut epithelium is up to 15 lm or more thick, densely ciliated and glandular, although not as deeply folded as in other members of the genus (Fig. 10).
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Figure 12. Callinera bergendali sp. nov. Camera lucida drawing of transverse section through the mid-cerebral region to show dorsal and ventral cerebral commissures.
The junction between foregut and intestine is marked by a change in the nature of the gland cells. The intestinal epithelium, up to 30 lm or more thick, histologically resembles that described for other species of Callinera. There are no lateral diverticula or pouches, the intestine essentially forming a simple tubular canal. The general organisation of the gut in the Hong Kong species shows no major differences from that described for the Scandinavian or British taxa. Blood system. The blood system in the present species is much more simple than in other species of Callinera. In the head, a pair of spacious thin-walled lateral cephalic lacunae meet in front of the proboscis pore by a wide transverse connective. The two cephalic lacunae continue posteriorly through the cerebral ring (Fig. 12), with almost no reduction in size, for most of the foregut region extending internal to the body wall inner circular muscle layer on either side of the rhynchodaeum and dorsolateral to the alimentary tract but moving outside the muscle layer (Fig. 10) just before the excretory system commences. In the intestinal portion of the body the lacunae develop thicker walls and gradually become smaller as they approach the rear of the rhynchocoel (Fig. 11). Behind the muscular bulb of the rhynchocoel, as the intestine expands to occupy more of the available body space, the two lateral vessels become very compressed, to the extent that in many parts of the intestinal region they are virtually indiscernible. There is no evidence of pseudometameric transverse connectives linking the lateral vessels in the intestinal region, nor is there any trace of a mid-dorsal blood vessel. Nervous system. The brain and lateral nerve cords are situated between the epidermal basement membrane and outer circular body wall muscle layers. The cerebral ganglia are well developed and transversely linked by a single dorsal and ventral commissure, respectively 8–10 lm and 20–22 lm thick (Fig. 12). In one specimen
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dorsal and ventral commissures are situated at the same level, in the other the dorsal is anterior to the ventral. A delicate inner neurilemma is distinguishable, but there is no outer neurilemma. Neither neurochords nor neurochord cells are present. The longitudinal nerves extend back from the rear of the ventral cerebral ganglia in a lateral position (Figs 10, 11). From the rear of each ventral cerebral lobe, close behind the ventral commissure, a distinct nerve leads back for a short distance and then turns dorsally to fuse with its partner, forming a ventral ganglionic mass below the rhynchodaeum. Almost immediately, this neural mass divides to form a pair of large (20 lm diameter) buccal nerves which continue posteriorly past the mouth, moving to a more ventrolateral position as they do so. Behind the mouth the nerves can only be traced in the parenchyma below the ventrolateral foregut margins for a short distance; their ultimate fate was not determined. From the rear of the dorsal commissure the single median dorsal nerve, which emerges to extend posteriorly through the foregut region (Fig. 10), divides into two (Fig. 11) close in front of the rhynchocoel muscle sac; the posterior limits of these nerves were not traced. Several distinct nerves run anteriorly from the front of the brain. They form a more or less continuous ‘layer’ immediately below the epidermal basement membrane, although individual nerves remain clearly distinguishable. Farther forwards the nerves become smaller and less obvious and are eventually impossible to find. Sensory organs. As in other species of Callinera, the present form possesses neither eyes nor cerebral sensory organs. A pair of lateral epidermal sensory organs is situated at the same level of the body as the nephridiopores. The organs appear as elongate lateral furrows, about 100 lm long, extending about 30 lm into the epidermis just above the lateral nerves. The epidermal tissues immediately adjacent to these furrows have a distinctly striated appearance but are not otherwise separated from them. Frontal glands and apical organ. Neither an apical organ nor frontal glands can be distinguished in the present species. Excretory system. The excretory system is well developed and extends for approximately 440 lm from the foregut into the anterior intestinal region. A single thick-walled (8–10 lm) ciliated collecting tubule extends dorsolaterally in the parenchyma on either side of the body, close above the lateral blood vessels (Fig. 10). In their anterior regions the tubules penetrate the blood vessels and are associated with gland-like masses hanging in each blood vessel lumen. The collecting tubules narrow posteriorly before turning dorsolaterally into the slender (6–7 lm overall diameter) efferent canals which lead through the body wall layers to small nephridiopores, located just behind where the foregut leads into the intestine and close in front of the rhynchocoel muscle sac. Reproductive system. All the specimens collected were sexually immature. Systematic discussion. The Hong Kong species, together with Callinera buergeri and C. monensis Rogers, Gibson & Thorpe, 1992, form a distinct and well-supported clade in Sundberg & Hylbom (1994); C. buergeri forma grandis Bergendal, 1903, was identified by Rogers et al. (1992) as a distinct species and listed as C. grandis Bergendal, 1903, by Gibson (1995). Sundberg & Hylbom (1994) chose not to recognize the
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specific status of this form but had it been included in their analyses it too would have belonged in the same clade. One of the major characters identifying this clade as a monophyletic group is the powerfully developed rhynchocoel muscle sac, formed from the posterior circular muscle layer. Rogers et al. (1992) tabulated the major anatomical characters that could be used to distinguish between the three species of Callinera then known. The present species differs from C. grandis and C. monensis in possessing lateral sensory organs near the nephridiopores, from C. buergeri and C. grandis in possessing only a single dorsal cerebral commissure, and from C. grandis in lacking subepidermal glands, in its cephalic blood supply consisting of two spacious lacunae and in its foregut nerves fusing just in front of the mouth to form a short single median ventral nerve. The blood supply in the head of the present species also differs from that of C. buergeri and C. monensis, in both of which there is essentially a single thin-walled lacuna irregularly subdivided into four longitudinal channels. These differences justify the Hong Kong form being identified as a new species, Callinera bergendali. Genus Carinina Hubrecht, 1885 Diagnosis. Hylbom (1957: 541) gave the following diagnosis for the genus Carinina: “Brain and lateral nerves situated in the epidermis; epidermis very high; basement membrane thin; body musculature consisting of outer circular, longitudinal and inner circular muscle layer; a thin longitudinal muscle plate present between the proboscis sheath and the gut; muscular wall of the proboscis sheath with circular muscle layer only; excretory organs with gland-like anterior parts in close connection with the lateral blood vessels, nephridial canals running backwards from the glandlike portions inside the inner circular muscle layer, in their posterior part turning at right angles towards the body surface where they open in an excretory pore; two proboscis nerves running forwards from the ventral commissure of the brain entering the rhynchodaeum in the tip of the head.” In his key to the tubulanid genera Hylbom separates Carinina from Callinera and Tubulanus by the position of the brain and lateral nerve cords in the epidermis, rather than between the epidermal basement layer and body wall outer circular muscle layer. Carinina sinensis sp. nov. (Figs 13–15) HK sp. 1 in Sundberg & Hylbom (1994) Type specimen. Holotype: immature female, series of transverse sections from the anterior tip back into the posterior intestinal region (5 slides), SMNH 4892. Type locality. Hoi Ha Wan (Location 1, Fig. 1), south-west of Flynn Point, 7 m depth in shell sand. Etymology. The specific epithet is the New Latin word sinensis (= of China) and indicates the geographical region from where the species was obtained. External features. The single specimen obtained was about 7–8 mm long, with a transparent body through which the intestine was clearly visible posteriorly. The
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Figure 13. Carinina sinensis sp. nov. Camera lucida drawing of transverse section through the cephalic region.
appearance of the specimen in life was virtually identical to that described for Parahubrechtia jillae gen. et sp. nov., with which it was found, and the two taxa could only be distinguished after histological examination. Body wall, musculature and parenchyma. The cephalic epidermis (Fig. 13) is 60–66 lm tall dorsally and ventrally, mostly rather less on the lateral margins. Throughout much of the head distinct radial fibres extend in the proximal half of the epidermis between the cephalic nerves; these fibres appear to radiate from the outer circular muscle layer. Anteriorly no gland cells are distinguishable, but towards the front of the brain isolated acidophilic glands begin to appear within the middle to proximal levels of the epidermis. In the brain region (Fig. 14) the non-neural parts of the epidermis are reduced to a height of only 15–25 lm, and the acidophilic glands begin to increase their density. Other isolated refractile glands, located distally, are also evident in the epidermis of the brain region. Behind the brain, epidermal height again increases to 25–50 lm (Fig. 15) and the acidophilic glands are densely packed and form a distinct proximal layer extending for almost 1 mm post-cerebrally before they abruptly disappear. Throughout the intestinal region the epidermis is gradually reduced posteriorly to a maximum height of some 20–25 lm. The epidermal basement layer throughout the body is thin. The body wall musculature comprises outer circular and inner longitudinal layers, respectively 4–5 lm and 15–30 lm thick in the foregut region of the body. An inner circular layer, 4–5 lm thick, is present throughout most of the foregut region (Fig.
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Figure 14. Carinina sinensis sp. nov. Camera lucida drawing of transverse section through the posterior cerebral region to show the mouth, cerebral sensory organs and arrangement of the blood system.
15), commencing just behind the mouth. The outer circular muscles are reduced to a thickness of 2–3 lm in the intestinal regions, but the longitudinal layer may be 60 lm or more wide and the inner circular musculature forms a delicate layer, one or two fibres thick, enclosing the intestine behind the end of the rhynchocoel. A layer of longitudinal muscle fibres, 2–4 lm deep, extends between the rhynchocoel and gut (Fig. 15) for most of the foregut length, but this layer ends anteriorly at the proboscis insertion, located behind the mouth, and in its place there is a transverse band of muscle fibres derived from both body wall circular muscle layers. The transverse band, up to 7–8 lm or more thick, effectively separates the body wall longitudinal muscle layer into dorsal and ventral portions above the mouth, where it passes under the rhynchodaeal wall. Longitudinal fibres are missing from the lateral body margins (Fig. 14). The inner circular layer disappears in front of the mouth, but the transverse muscle band continues forwards through the cerebral ring to contribute to a band of circular fibres enclosing the anterior portion of the rhynchodaeum (Fig. 13). Fibres radiate outwards from this rhynchodaeal muscle layer towards the lateral cephalic borders. No dorsoventral muscle bundles can be distinguished in the intestinal regions, and parenchymatous connective tissues are barely developed.
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Figure 15. Carinina sinensis sp. nov. Camera lucida drawing of transverse section through the foregut region.
Proboscis apparatus. The proboscis pore opens ventrally just behind the tip of the head. It leads into a rhynchodaeum (Fig. 13) whose ciliated epithelium for most of the cephalic length is 30–55 lm in height and contains isolated acidophilic and basophilic gland cells. Just behind the proboscis pore two of the nerves that comprise the cephalic neural layer turn inwards and enter the rhynchodaeal epithelium. These nerves can be traced the full length of the rhynchodaeum (Figs 13, 14), through the proboscis insertion and into the proboscis. The rhynchodaeum, with an overall diameter of some 120 lm, occupies much of the cephalic space but is somewhat reduced in diameter as it passes through the cerebral ring. Here its epithelium is also reduced to a maximum height of 12–15 lm. The rhynchodaeum is about 45 lm wide and 85 lm in dorsoventral height as it approaches the front of the mouth, gradually becoming smaller as it passes the oral region until, just in front of the proboscis insertion, it forms a narrow tubular canal about 30 lm in overall diameter, enclosed by a layer of circular muscle fibres. The proboscis insertion is situated post-orally. The rhynchocoel is approximately half the length of the body, its wall containing mainly circular fibres which form a layer 8–10 lm thick. The fibres of the rhynchocoel circular musculature cannot be distinguished from those of the body wall inner circular layer mid-dorsally, but on either side of this region isolated longitudinal muscle fibres run between the rhynchocoel and inner circular muscle layers. The proboscis (Fig. 15) contains two histologically distinct regions. In the retracted position, the anterior and longer portion is about 115 lm in overall diameter and contains a glandular epithelium up to about 15 lm thick, an outer circular muscle
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stratum no more than 3–4 lm across, an inner longitudinal muscle layer at most 15 lm deep, and a delicate inner lining. The two proboscis nerves are distinct and run in the proximal portion of the epithelium on either side of the proboscis (Fig. 15). Farther back, this portion of the proboscis is slightly larger, with an overall diameter of 125–130 lm, its epithelium is, in places, 25–30 lm or more thick, but its longitudinal muscle layer is progressively reduced to a maximum thickness of only 5–6 lm. In contrast, the posterior portion of the proboscis has an epithelium with a distinctly vacuolate appearance, no proboscis nerves can be distinguished, and both muscle layers are reduced to only one or two fibres thickness and are often difficult to see. Alimentary canal. The small mouth (Fig. 14) is situated below the rear portion of the brain. It opens into a foregut whose richly glandular and densely ciliated epithelium is, at first, up to some 30 lm thick, and moderately deeply folded (Fig. 15). Farther back, however, the foregut wall is unfolded and the epithelium reduced to a thickness of 15 lm or less; this posterior half of the foregut forms a dorsoventrally compressed canal arching below the ventral half of the rhynchocoel. The junction between foregut and intestine is marked by the change in gland cell appearance, presence of food vacuoles in the epithelial cells and sparse ciliation. The anterior portion of the intestine, like the foregut with which it communicates, arches below the rhynchocoel as a wide but compressed tubular canal. Behind the end of the rhynchocoel, however, the intestine enlarges to occupy most of the body space between the gonads and lateral blood vessels and its epithelium is up to 45 lm or more in height. The intestine does not possess lateral pouches or diverticula. Blood system. A pair of spacious lateral cephalic lacunae in the head (Fig. 13) meet anteriorly by a broad transverse connective crossing above the proboscis pore. The lacunae are irregularly crossed by isolated muscle fibres or connective tissue fibrils, so that in some sections there appear to be more than two blood channels. Near the front of the brain the cephalic lacunae meet below the rhynchodaeum by a ventral connective, which continues posteriorly as a median ventral channel. This channel, at least anteriorly, is irregularly subdivided by connective tissue and muscle fibrils. There are three longitudinal lacunae in the brain region; the lateral cephalic lacunae continue back, one on either side of the rhynchodaeum, whereas the ventral lacuna enlarges to occupy much of the ventral half of the body but is separated from the lateral lacunae and rhynchodaeum by the transverse muscle band. Towards the rear of the brain, as the oral epithelium bulges inwards, the ventral lacuna becomes compressed and then separates to form two lacunae, one running on either dorsolateral margin of the foregut. There are thus four lateral blood lacunae, arranged in dorsal and ventral pairs separated by transverse muscles, in the mouth region (Fig. 14). Just behind the mouth, however, the ventral lacunae end blindly. The dorsal lacunae continue on either side of the rhynchodaeum until, just before the proboscis insertion, they become less spacious and move to a dorsolateral position on either side of the foregut, internal to the body wall inner circular muscle layer. They continue in this position for the remaining length of the foregut and anterior intestine but, behind the end of the rhynchocoel, expand again to form a pair of large lateral channels running on either side of the intestine and outside the inner circular muscle layer. There are no pseudometameric transverse connectives nor a median dorsal vessel.
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Nervous system. The cerebral ganglia and lateral nerve cords are situated in the proximal portion of the epidermis. The brain lobes are large and well developed relative to the diameter of the head (Fig. 14). Dorsal and ventral lobes are of similar size, both being incompletely enclosed by a distinct outer neurilemma, which has an appearance of concentric layers of connective tissue fibres. The ventral lobes are located ventrolaterally, the dorsal laterally. Posteriorly the dorsal lobes reach above the mouth (Fig. 14). A distinct inner neurilemma separating the fibrous and neuroganglionic tissues of the brain lobes is also present, though thinner than the outer layer. The ventral cerebral commissure, about 40 lm thick, is anterior to the dorsal commissure, which has a maximum thickness of 15 lm. In front of and behind both commissures, acidophilic glands histologically identical with glands found in the remaining epidermis are distributed between the neuroganglionic cells of the brain (Fig. 14); close anteriorly and posteriorly to the commissures, these glands are also enclosed by the outer neurilemma. Farther from the commissures, their separation from the remaining epidermal tissues becomes less distinct. No evidence of either neurochord cells or neurochords could be found in the brain or lateral nerves. The lateral nerves, whose fibrous cores are 40–45 lm in diameter, extend posteriorly in the proximal epidermis on either side of the body (Fig. 15). A distinct zone of several more or less discrete cephalic nerves extends anteriorly from the front of the brain in the proximal portion of the epidermis (Fig. 13). These nerves can be followed almost to the tip of the head. Among the other peripheral nerves that can be distinguished is a pair of nerves leading posteriorly from the rear of the ventral commissure, and passing on either side of the oral epithelium. The ultimate fate of these nerves could not be followed but they comprise the buccal or foregut nerve supply (Fig. 14). A median dorsal nerve (Fig. 15) leading from the dorsal cerebral commissure can be traced back at the proximal border of the epidermis into the anterior intestinal region. Sensory organs. The present species does not possess eyes. In the cerebral region a wide but shallow indentation on either side of the body leads to a distinct lateral furrow, some 30 lm deep. The cilia of the furrows are long (15 lm) and dense. From the ventral margin of each furrow a ciliated cerebral canal, 15–18 lm in diameter, leads inwards between the dorsal and ventral fibrous cores of the brain lobes, then turns backwards to continue posteriorly for approximately 200 lm before ending blindly. As it extends posteriorly, each canal gradually moves to a more dorsolateral position. Each cerebral canal, throughout its length, is surrounded by neuroganglionic tissues histologically indistinguishable from those of the brain lobes (Fig. 14), and there is no evidence of glandular tissues associated with any part of the canal. These structures constitute the cerebral sensory organs but appear to have a much more simple construction than those of most other nemerteans. No other sensory structures could be distinguished in any part of the body. Frontal glands and apical organ. The present species possesses neither an apical organ nor frontal glands. Excretory system. The excretory system commences in the intestinal portion of the body, close behind the posterior limit of the distinct acidophilic glandular band found in the epidermis. Anteriorly, the system comprises a short glandular mass
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lying close to the lateral blood lacunae; from the rear of this mass a single collecting tubule leads posteriorly for about 200 lm, then turns outwards to form a wide (10–15 lm) efferent canal that leads dorsolaterally to a single nephridiopore on each side of the body. Reproductive system. The single specimen is an immature female. The ovaries are distributed in a single dorsolateral row on either side of the body, dorsal to the lateral blood lacunae, commencing close behind the end of the rhynchocoel. Several ova in different stages of oogenesis are present within each ovary. Systematic discussion. Sundberg & Hylbom’s (1994: fig. 9) phylogenetic analyses show that HK sp. 1 belongs in the same clade as Carinina arenaria Hylbom, 1957, C. atavia (Bergendal, 1902), C. coei Hylbom, 1957, C. grata Hubrecht, 1887, C. remanei (Nawitzki, 1931) and C. wijnhoffae Kulikova, 1984; Carinina grata is the type species for the genus, which currently contains 14 described forms (Gibson, 1995), and there is no doubt that the present form from Hong Kong belongs in the same genus. Reference to the character matrix given by Sundberg & Hylbom (1994: Table 2) shows that HK sp. 1, whilst sharing many anatomical features with the other Carinina species, can be distinguished from all of them. For example, C. buergeri Joubin, 1902, and C. remanei possess two dorsal cerebral commissures; statolith-like structures are present in the brain of C. arenaria, C. buddenbrocki (Friedrich, 1935a), C. coei, C. heterosoma Mu¨ller, 1956, C. poseidoni Friedrich, 1935b, and C. remanei, whilst there are no rhynchodaeal nerves in C. pacifica Friedrich, 1970. Other morphological characters, too, can be used to distinguish the present taxon from one or more of the known Carinina species; these include the number of dorsal nerves, presence of rhynchocoel blood vessels, the organisation of the body wall muscle layers, the position of the lateral blood vessels in relation to the body wall inner circular musculature, and the arrangement of the blood system in the oral region. Differences that can be used to separate the known species of Carinina are summarized in Table 1. It is concluded that the Hong Kong form is new to science, and it is accordingly named Carinina sinensis sp. nov.
Genus Tubulanus Renier, 1804 Diagnosis. The genus Tubulanus, according to Sundberg & Hylbom’s (1994: Table 4) character matrix, contains species with the following anatomical features: length at the onset of sexual maturation 2–10 cm; coloured, usually with a conspicuous pattern; head furrows present; body wall musculature consisting of outer and inner circular and middle longitudinal layers; muscle crosses present between outer and inner circular muscles in some species; diagonal muscles present; cerebral sensory organs consisting of ciliated pits or ciliated canals in the epidermis; side organs present in foregut region in some species; cephalic region with nerve layer; two nerves in rhynchodaeal epithelium; proboscis nerves present; brain and lateral nerves situated between epidermal basement membrane and outer circular muscles; epidermal basement membrane usually thick; nervous system with neither neurochords nor neurochord cells; buccal nerves present and paired; intestine with shallow lateral diverticula; rhynchocoel wall with circular muscles only; proboscis musculature with outer longitudinal and inner circular layers; circular muscle layer in rear end of rhynchocoelic or in nephridial regions
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T 1. Summary of some of the anatomical features that can be used to distinguish between species of the palaeonemertean genus Carinina. Based on data contained in Sundberg & Hylbom (1994) Species of Carinina
A
B
C
D
E
F
G
H
antarctica Bu¨rger, 1904 arenaria Hylbom, 1957 atavia (Bergendal, 1902) buddenbrocki (Friedrich, 1935) burgeri Joubin, 1902 coei Hylbom, 1957 grata Hubrecht, 1887 heterosoma Mu¨ller, 1965 littorea Korotkevich, 1982 mawsoni Wheeler, 1940 pacifica Friedrich, 1970 poseidoni Friedrich, 1935 remanei (Nawitzki, 1931) wijnhoffae Kulikova, 1984 sinensis sp. nov.
? 2 1 2 ? 2 2 1 2 1 1 2 1 1 1
2 1 1 ? ? 1 0 0 1 2 0 1 1 1 0
0 0 0 0 ? + 0 0 + 0 0 0 0 0 0
? 0 0 0 + 0 0 0 ? 0 0 0 0 0 0
? + 0 + ? + 0 + ? ? 0 + + 0 0
? 0 0 ? ? 0 0 + ? 0 0 ? 0 + 0
? 1 1 1 2 1 1 1 ? ? ? 1 2 1 1
? 0 1 ? ? 1 0 0 ? 0 2 2 2 1 2
A: B: C: D: E: F: G: H:
Median dorsal nerve supply consisting of upper nerve only (1) or with both upper and lower nerves (2). Lateral blood vessels anteriorly run internal to body wall inner circular muscle layer but further back move outside these muscles (0), remain entirely internal to inner circular musculature (1) or are completely external to the muscle layer (2). Rhynchocoel blood vessels present (+) or absent (0). Eyes present (+) or absent (0). Statoliths in cerebral ganglia present (+) or absent (0). Cephalic glands present (+) or absent (0). Dorsal cerebral lobes transversely linked by one (1) or two (2) dorsal commissures. Blood system in mouth/anterior foregut region consisting of two lateral vessels only (0), lateral vessels developed to form vascular plexus around foregut (1) or with four lateral vessels not forming plexus (2).
strongly developed; gland-like anterior part of excretory system entering lateral blood vessels; blood vascular system without mid-dorsal vessel; eyes absent; sexes separate. Body wall muscle crosses and the presence of proboscis nerves are regarded as possible synapomorphies by Sundberg & Hylbom (1994). This diagnosis broadly agrees with the traditional definition of the genus given by Gibson (1994), although certain additional characters included by Gibson are shown in italics in the diagnosis above. Tubulanus hylbomi sp. nov. (Figs 16–20) HK sp. 5 in Sundberg & Hylbom (1994) Type specimens. Holotype: immature, series of transverse sections through anterior body back to intestinal region, (13 slides), paratypes: immature, series of transverse sections through anterior body region, (19 slides) and through anterior body back to intestinal region, (18 slides), SMNH 4893. Type locality. South-east of Tap Mun, 17 April 1992, trawled from 33 m depth in fine clay (Taylor, 1992: Trawl 13 [Location 2, Fig. 1]). Additional locations. South-east of Tap Mun, 28 April 1992, trawled from 5 m depth in rubble and mud (Taylor, 1992: Trawl 51 [Location 3, Fig. 1]), and intertidal in mud at Hoi Ha Wan (Location 1, Fig. 1).
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Figure 16. Tubulanus hylbomi sp. nov. Drawing to show the cephalic lobe and anterior colour pattern, viewed dorsally, based on sketches made of a living specimen.
Etymology. The species is named after Richard Hylbom as a tribute to his work on palaeonemerteans. External features. Two of the three specimens obtained were fragmented. The only intact individual was about 35 cm long, with a maximum width of 3 mm. The body was somewhat flattened in cross-section, with the dorsal surface more rounded. The head was clearly demarcated from, although the same width as, the adjacent portion of the body, which gradually tapered posteriorly. The general colour was a light brown, marked with two lateroventral longitudinal white stripes which anteriorly extended to the rear of the head, and a median dorsal white stripe which almost reached the cephalic tip (Fig. 16) and here formed a cross. The margins of the head were also white and unevenly spaced white bands were present throughout the length of the body, commencing about 2 cm behind the head. A white band immediately in front of the mouth, which had white borders, demarcated the posterior limit of the head. Neither eyes nor cephalic furrows were visible in life, although the proboscis pore was distinguishable near the anterior tip of the head. Body wall, musculature and parenchyma. The epidermis is mostly 150–170 lm thick, but tends to be much less than this along the lateral body margins or where locally folded. Coarsely granular acidophilic glands are scattered throughout the epidermis in the head and foregut regions but farther back form an almost continuous layer, 30–75 lm deep, encircling the body; the glands, with tracts of secretion extending to the epidermal surface, are mainly situated proximally but are separated from the epidermal basement layer by a clear zone about 30 lm wide. These acidophils are completely missing from the extreme anterior cephalic region and posterior to the excretory pores. At least two other types of epidermal glands can be distinguished, one basophilic with homogeneous to finely particulate contents, the other finely granular and staining with Orange G; neither of these gland types, however, forms
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Figure 17. Tubulanus hylbomi sp. nov. Camera lucida drawing of transverse section through the cephalic region to show the well developed cephalic glands, rhynchodaeum and blood system.
a distinct layer, instead being widely scattered between the proximal and distal portions of the epidermis. The connective tissue epidermal basement layer, mostly 5–30 lm thick depending upon local contraction, has a proximal mesh-like appearance and distally extends into the basal portion of the epidermis. Along the lateral cephalic margins this basement layer is often so delicate as to be almost indiscernible (Fig. 17). The body wall musculature comprises outer circular, middle longitudinal and inner circular layers which are respectively some 15–30 lm, 100–150 lm and 3–15 lm thick. The longitudinal muscle fibres are arranged into fasciculated bundles. The inner circular muscles laterally and ventrally surround the foregut and intestine, but dorsolaterally merge with the circular muscles of the rhynchocoel wall (Figs 18, 19). A plate of horizontal longitudinal muscles, up to about 45 lm thick above the gut, extends between the rhynchocoel and gut walls. The fibres forming this layer also extend around the foregut wall between its epithelial basement membrane and the inner circular musculature (Fig. 18), but are here very much more weakly developed, rarely more than 6–8 lm deep, and ventrally are reduced to small isolated fibre bundles adjacent to the foregut wall. These horizontal muscles split up above the anterior part of the mouth, forming isolated bundles of fibres that become separated from the oral epithelium by bands of transverse muscles up to 35–40 lm thick; these transverse muscles have their origin among the proximal lateral fibres of the body wall longitudinal musculature. No muscle crosses were found between the outer and inner body wall circular muscle layers, as reported for several species of Tubulanus. In the head, the two outermost body wall muscle layers are significantly reduced, the circular layer to about 15 lm in maximum thickness, the longitudinal layer to between 7–45 lm. The inner circular musculature also extends into the head, where it forms a transverse plate of fibres 7–15 lm across passing below the cephalic blood lacunae and between the frontal gland lobules; only mid-ventrally does this muscle layer run adjacent to the longitudinal musculature. Parenchymatous connective tissues are moderately extensive, particularly on either side of the foregut, anterior intestine and rhynchocoel.
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Figure 18. Tubulanus hylbomi sp. nov. Camera lucida drawing of transverse section through the foregut region.
Figure 19. Tubulanus hylbomi sp. nov. Camera lucida drawing of transverse section through the anterior intestinal region.
Proboscis apparatus. The proboscis pore opens subterminally. It leads into a tubular rhynchodaeum whose ciliated epithelium is at first histologically similar to the adjacent epidermis, except for lacking gland cells. Behind the proboscis pore the rhynchodaeal epithelium varies from 15 to 75 lm in thickness, depending upon the
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degree of folding, but farther back in the head becomes progressively compressed by the development of the frontal glands and is in places less than 2–3 lm across. The posterior portion of the rhynchodaeum is identical in appearance to the frontal glands situated immediately beneath its epithelium, but under high power a delicate basement membrane can often be distinguished separating the rhynchodaeal epithelium from the glands. The rhynchodaeum is surrounded by a layer of longitudinal muscle fibres (Fig. 17). The proboscis insertion is situated in the posterior cerebral region, close to the rear of the brain. The rhynchocoel wall contains only circular muscle fibres (Figs 18, 19), forming a distinct layer up to 45 lm or more thick. In the foregut region, the rhynchocoel occupies about 60% of the body diameter. The proboscis for most of its length is about 800 lm in maximum diameter when retracted. It is composed of a columnar epithelium 150 lm or more tall, an outer circular muscle layer 20–35 lm across, an inner longitudinal muscle layer 35–45 lm thick, and an inner lining layer (Fig. 18). The epithelium distally bears scattered ‘pads’ of basophilic rhabditoids about 5–6 lm tall and 15 lm in diameter; the pads are often arched in a semi-circular shape. There are two proboscis nerves, one on either side of the organ situated between the epithelium and circular muscle layer (Fig. 18); these nerves are not always distinguishable in the more posterior parts of the proboscis (Fig. 19). Scattered Orange G positive glands occur in the proximal half of the epithelium. The extreme anterior end of the proboscis is slightly wider than the remainder of the organ and, in places, is almost 1 mm in diameter. The epithelium lacks the rhabditoid pads in this region. The proboscis nerves arise from the inner face of the dorsal brain lobes. Alimentary canal. The mouth opens immediately behind the brain, although the oral groove in the epidermis extends forwards below the posterior brain region. The oral margins may protrude ventrally some 400 lm to give the appearance of thick ‘lips’. The buccal epithelium is folded, 90–150 lm or more tall, clad in short densely distributed cilia and richly provided with gland cells which are mainly basophilic. The foregut is spacious and for much of its length possesses deeply folded walls on all but the dorsal margin (Fig. 18); here, below the rhynchocoel, the epithelium is only 60–70 lm thick and not folded. Both the epithelial height and degree of folding are progressively reduced posteriorly, at the same time as the density of the basophilic gland cells is also diminished. The junction between foregut and intestine is marked by the appearance of long, sparsely distributed cilia and pyriform gland cells. The intestinal wall is mostly 100–140 lm thick. The intestine does not possess lateral diverticula and for much of its length forms a spacious, but somewhat dorsoventrally compressed, canal arching beneath the rhynchocoel (Fig. 19). Blood system. In the head a well developed lacunar network, flanking the rhynchodaeum, comprises a pair of large lateral channels which are irregularly subdivided by muscle and connective tissue fibrils (Fig. 17). Branches of the lacunae also extend and meet above the rhynchodaeum. Anteriorly, the lacunae meet by a slender transverse dorsal connective situated close behind the proboscis pore. Two large lateral lacunae enter the cerebral ring close to the inner borders of the brain lobes, but smaller dorsolateral branches are still present adjacent to the rhynchodaeal wall. Behind the ventral cerebral commissure, an outer ventrolateral lacuna appears on each side of the body in the parenchyma between the epidermal basement layer
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Figure 20. Tubulanus hylbomi sp. nov. Camera lucida drawing of transverse section through the cerebral region. Note the blood vessels running close to the cerebral sensory organs.
and the brain lobes (Fig. 20). These lacunae are spacious, up to 230–250 lm or more in maximum dimension, and are irregularly traversed by connective tissue and muscle fibrils. Farther back, as the cerebral sensory organs appear, the lacunae are divided into upper and lower branches by the cerebral organ nerve leading from the brain (Fig. 20). The lower branch on each side of the head runs close to the cerebral organ and is filled with a mixture of finely granular basophilic, coarsely granular acidophilic and vacuolar acidophilic material that appears to be secretory, rather than representing typical blood cells, as described from many other nemertean species; it is possible that this material is derived from the glands of the cerebral organs although the lacunae, whilst passing close to the organs, do not seem to have intimate contact with them. The two branches of the ventrolateral lacunae, towards the rear of the brain, meet to form a spacious channel which is further subdivided by muscle and connective tissue strands; branches of these lacunae are in connection with the main lateral blood channels, which continue back from the cephalic blood supply. In front of the mouth the blood system comprises a pair of large lateral lacunae flanking the rhynchocoel and buccal walls. Behind the mouth, further subdivision of the lacunae by connective tissue and muscle fibrils leads to the development of a foregut lacunar plexus (Fig. 18); this extends throughout the length of the foregut and into the anterior intestinal region. There is no mid-dorsal blood vessel, but a short distance behind the mouth branches of the main lateral lacunae lead towards and penetrate the ventrolateral rhynchocoel floor on either side. The rhynchocoel bodies (i.e. tissue protrusions enclosing blood vessels which penetrate the rhynchocoel wall) so formed have a flattened and rather lozenge-shaped appearance in sections and are about 15 lm by 75 lm in height and width respectively; they run back in the rhynchocoel wall for some 60–80 lm and then appear to end blindly. The vessels in these rhynchocoel bodies contain material similar to that seen in the lacunae adjacent to the cerebral organs. The blood system in the intestinal region essentially comprises a pair of large
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lateral lacunae, lined by an internal epithelium which is in places 15 lm or more thick. These lacunae, too, are sometimes subdivided by tissue strands, but for most of their length form single spacious channels on each side of the body (Fig. 19). No evidence of pseudometameric transverse connectives linking the lateral lacunae could be found in the intestinal region. Nervous system. The large and well developed brain lobes are situated ventrolaterally (Fig. 20). They are enclosed by a distinct connective tissue outer neurilemma, but there is no inner neurilemma separating the neuroganglionic and fibrous cerebral components. For most of their length the brain lobes are separated from the epidermal basement layer by discrete bundles of longitudinal muscle fibres, in places up to 40 lm thick, but these muscle bundles are missing below the ventral commissure and from the lateral brain margins. The single ventral commissure, 45–50 lm thick, is located anterior to the two dorsal commissures, both of which are much longer than the ventral and about 30 lm thick. All three commissures are located in front of the proboscis insertion. Several large nerve tracts can be distinguished emerging from the brain lobes. One pair, extending from the inner anterior surface of the dorsal lobes, forms the origin of the proboscis nerve supply; another pair, emerging somewhat farther back, forms the buccal nerves; and a third pair, leading from the outer ventrolateral surface of the dorsal lobes, innervates the cerebral sensory organs. Several nerves also lead anteriorly from both dorsal and ventral ganglia to form the cephalic neural layer, that extends between the outer circular muscle and the epidermal basement layers (Fig. 17); some of the nerves in this layer are 50 lm or more in diameter. The cerebral organ nerves fork into upper and lower branches soon after leaving the brain and enter the cerebral organs on their dorsal and ventral margins respectively. The dorsal and ventral brain lobes separate a short distance in front of the mouth, but the upper lobes continue posteriorly for some distance before terminating above the oral rim. The lateral nerve cords extend between the body wall outer circular muscles and the epidermal basement layer (Figs 18, 19). Neither the lateral nerves nor the brain lobes contain neurochord cells or neurochords. There is only a single, small, median dorsal nerve, external to the outer circular musculature, and the lower dorsal nerve found in many Tubulanus species could not be discerned. The large and distinct foregut nerves meet above the mouth by a single transverse commissure, 15 lm thick, before branching to form the foregut neural plexus. Several distinct nerves can be traced throughout the foregut length, running adjacent to the epithelial basement membrane (Fig. 18). Sensory organs. The present species does not possess eyes. The cerebral sensory organs, situated in the proximal portion of the epidermis, are large and distinct. Each opens to the exterior via a short ventrolateral ciliated canal leading inwards from the epidermal surface, located at a level just in front of where the dorsal and ventral cerebral lobes separate posteriorly (Fig. 20). The organs are large, up to about 170 lm in diameter and 420–450 lm long, posteriorly ending level with the front of the mouth. For most of their length the organs consist of neural tissues through which the ciliated cerebral canal extends directly backwards; proximal major and distal minor channels, similar to those described for several other nemertean species, are clearly visible in transverse section. Glandular components of the organs are mainly anterodistal in position and irregularly extend into the adjacent
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epidermis; there is no basement membrane separating the cerebral organs from the other epidermal tissues. Deep narrow longitudinal ciliated furrows on the head, not distinguishable in life, are somewhat variable in their position and appear to represent localized foldings of the body surface rather than having any sensory significance. Lateral sensory organs, reported from several species of Tubulanus, could not be found in the present form and no other sensory structures were found. Frontal glands and apical organ. The frontal glands are extremely extensive and fill most of the head between the proboscis pore and cerebral ganglia; some of the glands reach as far back as the mouth. The glands are arranged into large, irregularlyshaped and sized lobules (Fig. 17) filled with finely homogeneous and lightly basophilic cytoplasm. For much of the cephalic region the rhynchodaeal epithelium is histologically identical in appearance and in places appears to connect with these glands. The glands discharge to the exterior through the apical organ, which opens into the dorsal wall of the rhynchodaeum above the proboscis pore. The apical organ is more or less spherical, 75–90 lm in diameter and surrounded by a delicate layer of longitudinal muscle fibres. Excretory system. The excretory system is situated dorsolaterally in the anterior intestinal region of the body; the collecting tubules, mostly up to about 60 lm in diameter, are lined by an epithelium some 15 lm thick. The tubules run in the parenchyma between the body wall longitudinal musculature and lateral blood lacunae. In some sections there appear to be several smaller tubules on each side, whilst in others they unite to form one or two large ducts 150 lm or more in diameter. In the anterior region thin-walled pouches on either side protrude into the lacunar wall from the collecting tubules. Towards the rear of the system the collecting tubules lead to a large thin-walled chamber, in places more than 200 lm across, from which short but thick-walled efferent canals, some 45 lm in diameter, lead dorsolaterally to open via the nephridiopores. There appears to be only a single nephridiopore on each side of the body. Reproductive system. None of the specimens contained mature gonads, although in one individual small and isolated flask-shaped pouches, located dorsolaterally in the parenchyma of the intestinal region (Fig. 19) are apparently gonads. Evidence of ducts leading from these structures towards the body surface suggests that the individual might be post-spawning, but the sexuality of the species remains unknown. Systematic discussion. The present species forms a clade with several other Tubulanus, including the type species for the genus (Tubulanus polymorphus Renier, 1804) in the phylogeny of Sundberg & Hylbom (1994: Fig. 4). Since it possesses several anatomical features that are traditionally associated with the taxon, we place the Hong Kong form in the genus Tubulanus. A comparison between the characters and their states for the 11 species shown in Sundberg & Hylbom’s (1994: Table 2) character matrix table shows that, excluding the present form, all the taxa share the following features, apart from those for which a particular character state is unknown (listed in parentheses): the head is bluntly rounded and possesses neither eyes (no data for T. nothus, although it is probably eyeless) nor cephalic sensory pits; the thickness of the epidermis relative to the body diameter in the midgut region is >0.05; the body wall musculature comprises outer circular, middle longitudinal and inner circular layers; the cerebral
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sensory organs are situated in the epidermis; excretory organs are present with the canal outside the body wall inner circular muscle layer (no data for T. floridanus Coe, 1951); there are neither neurochord cells nor statoliths in the brain lobes; the head possesses a well developed neural layer rather than four large and distinct nerves (no data for T. punctatus); proboscis nerves are present; the proboscis insertion is situated in the brain region (no data for either T. floridanus or T. punctatus); the proboscis musculature comprises outer circular and inner longitudinal layers; the rhynchodaeal epithelium is glandular; the rhynchocoel is less than the full body length (not recorded for T. capistratus or T. superbus); the brain and lateral nerve cords are situated between the epidermal basement layer and the body wall outer circular muscles; the ventral cerebral commissure is thicker than the dorsal; finally, the intestine does not possess lateral diverticula (no data for T. floridanus or T. punctatus). The present species also shares most of these features, although in their table 2 Sundberg & Hylbom (1994) indicate that in HK sp. 5 the proboscis insertion is located behind, rather than in, the brain region (Character 42, State 2); in the present studies it is evident that the insertion is positioned in the posterior cerebral region and a distinction between States 1 and 2 for this character becomes less obvious and is not regarded as necessarily significant. One feature found in the present species, however, differs from that described for the other palaeonemerteans in this group, namely that an incomplete layer of longitudinal muscle fibres is present between the brain lobes and the epidermal basement layer. Gibson (1995) lists 30 species of Tubulanus currently regarded as valid, 19 of which are known to possess a distinct colour pattern (there is no information on the external features of T. holorhynchocoelomicus Friedrich, 1958), though not all are either fully or adequately described. The body coloration of the nine Tubulanus species being compared with the present form are summarized in Table 2. The colour pattern of the Hong Kong species differs from that reported for most of these in that T. polymorphus and T. theeli are uniformly coloured with neither longitudinal stripes nor transverse bands, Tubulanus floridanus and T. rubicundus have transverse bands but no longitudinal stripes, T. punctatus and T. superbus possess four longitudinal stripes including a median ventral one, and T. nothus has a characteristic colourless head marked with a pair of black patches. The present species can be distinguished from the remaining two taxa in that T. annulatus possesses muscle crosses between the two body wall circular muscle layers and has both upper and lower dorsal nerves, whilst T. capistratus has lateral sensory organs, no buccal nerves and both circular and longitudinal muscle layers in its rhynchocoel wall. Reference to Sundberg & Hylbom’s (1994: table 2) character matrix for all of the species listed in Table 2 that differ from the present form in colour pattern shows that they also differ in several anatomical features from the Hong Kong taxon, which is accordingly described as a new species, Tubulanus hylbomi. Tubulanus longivasculus sp. nov. (Figs 21–23) HK sp. 6 in Sundberg & Hylbom (1994) Type specimens. Holotype: mature female, series of transverse sections through the anterior end of the body (27 slides), paratype: mature male, series of transverse sections through the foregut/intestinal region (23 slides), SMNH 4894.
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T 2. Summary of the body coloration of the nine species of Tubulanus being compared with the present species from Hong Kong Species
Coloration
Tubulanus annulatus
Overall colour vivid brick-red, orange-red, garnet-red or brownish-red, marked with mid-dorsal and lateral longitudinal white stripes and transverse white bands; ventral surface paler than dorsal and, apart from the first 2–3 bands, all are more or less equidistantly spaced. Cephalic lobe with transverse white band. Overall colour rich deep brown or greyish-black, posteriorly paler and yellowishbrown, with slender mid-dorsal and lateral longitudinal white stripes, lateral stripes much broken up anteriorly, with 200 or more transverse white bands. Overall colour brown with series of very narrow transverse bands, most of which completely encircle the body, without longitudinal stripes. Head colourless, marked with pair of crescentic black patches near anterior margins, dorsal body dark reddish-brown, ventral paler orange-brown fading to yellowish anteriorly and posteriorly. White dorsal median and lateral stripes present, usually with an inconspicuous median ventral stripe too. Forty or more white bands encircle body, occasional bands doubled, first three situated some distance in front of remainder. Body uniformly reddish- or orange-brown, paler towards posterior, without colour pattern. Body generally blackish-brown, sometimes chestnut-brown or brownish-yellow, fading posteriorly, ventral surface paler than dorsal. White band across head sometimes appearing as row of dots. With numerous transverse white bands more or less equidistantly spaced, bands mostly broad and narrow rings alternating. With mid-dorsal, mid-ventral and lateral white dotted longitudinal stripes, though these tend to be somewhat obscure. Dorsal and ventral body surfaces strongly coloured cherry-red, sometimes with purplish or fire-red tinge dorsally. Middle of head marked with pale yellow bar and pale yellow margins. Similar narrow pale yellow band behind mouth, followed after 10–12 mm by second band twice as thick, then after about 20 mm thicker and thinner bands alternate along body at intervals of about 4 mm. Under high power, groups of bands can be seen to consist in turn of very thick, thin, moderately thick, thin and very thick bands in regular sequence. General colour rich dark brown, reddish-brown, scarlet or cherry-red, with middorsal, mid-ventral and lateral longitudinal white or yellowish-gold stripes and large numbers (up to 200 or more) transverse white bands. Occasional bands may appear doubled, first three bands widely spaced, remainder close together and more or less equidistant. Body uniformly dark reddish-brown, without colour pattern.
Tubulanus capistratus Tubulanus floridanus Tubulanus nothus
Tubulanus polymorphus Tubulanus punctatus
Tubulanus rubicundus
Tubulanus superbus
Tubulanus theeli
Type locality. Western side of north tip of Flat Island (Location 4, Fig. 1), collected by SCUBA diving by PS, 7 m depth on fine to medium shelly sand with some mussel beds on top; the specimen was creeping about on the sediment surface. Erymology. The specific epithet, a composite of the Latin words longus (long) and vas (a vessel), refers to the unusually long rhynchocoelic blood vessel of the species. External characters. The single complete specimen obtained was more than 60 cm long. The rounded head was clearly demarcated from the remainder of the body and bore cephalic furrows which, though not evident in life, are clearly distinguishable in histological preparations. The general colour was brown, paler ventrally, marked
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Figure 21. Tubulanus longivasculus sp. nov. Drawing to show the colour pattern and appearance of the anterior end of the specimen.
Figure 22. Tubulanus longivasculus sp. nov. Camera lucida drawing of transverse section through the foregut region.
with two distinct pale brown dorsal longitudinal stripes (Fig. 21). There were also indistinct transverse bands and the lateral body margins were white. Body wall, musculature and parenchyma. In the foregut region the epidermis varies between 200 and 350 lm or more in height (Fig. 22) but is less than this in the
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Figure 23. Tubulanus longivasculus sp. nov. Camera lucida drawing of transverse section through the cerebral region. Note the bundles of longitudinal muscle fibres which intrude between the cerebral ganglia and the epidermal basement layer.
cephalic and posterior body regions. Several types of epidermal glands can be distinguished, arranged into distal and proximal zones. Strongly positive acidophilic glands, forming a dense proximal ‘layer’ encircling the body and extending for more than half the epidermal height, first appear in the foregut region at about the level of the rhynchocoel bodies (see Blood system, below). Their number gradually diminishes posteriorly. The connective tissue basement layer, with a finely striated appearance and radially orientated mesh-like fibres, is in places up to 90 lm or more thick (Fig. 22). A thin but distinct darker-staining membrane interfaces between the epidermis and this layer. Radial connective tissue fibres extend from the basement layer for up to about 60 lm into the epidermis at more or less regular intervals around the body. The body wall musculature comprises outer circular, middle longitudinal and inner circular layers (Fig. 22). In the foregut region these are respectively some 30 lm, 230 lm and 45–50 lm across, whereas in the intestinal regions the widths of these muscle coats are in comparison some 15–25 lm, 180–190 lm and 100 lm at most. A horizontal plate of longitudinal muscle fibres, 45–50 lm thick, extends between the gut and rhynchocoel; these muscles continue around the foregut between the gut epithelium and body wall inner circular muscle layer (Fig. 22) but laterally and ventrolaterally tend to be thinner (10–15 lm) and are ventrally arranged in isolated bundles of fibres running in the parenchyma. The muscle layer posteriorly reaches well into the intestinal region. Above the mouth the horizontal muscles break up into separate bundles, ventrolateral and lateral to the proboscis insertion, and are separated from the buccal wall by a loose layer of transverse muscle fibres crossing the body between the proximal portions of the body wall longitudinal musculature. The bundles of longitudinal fibres continue in front of the mouth, gradually expanding dorsoventrally until in the brain region they form a distinct but dorsally incomplete layer flanking the proboscis insertion (Fig. 23). The layer
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continues anteriorly into the head, extending on either side of the rhynchodaeum, where it ventrally merges with the blocks of body wall longitudinal muscles that run anteriorly from between the brain lobes. The longitudinal muscles running next to the rhynchodaeum are up to 60–70 lm thick but farther forwards are less strongly developed. In the head, outer circular and middle longitudinal body wall muscle layers are respectively about 15 lm and 45 lm in maximum thickness, and there is no trace of the inner circular musculature. Delicate bundles of dorsoventral fibres cross the head between the frontal gland lobules. Parenchymatous connective tissues are moderately extensive throughout the postcerebral regions of the body. Proboscis apparatus. The proboscis pore is subterminal. It opens into a rhynchodaeum whose wall is at first densely ciliated, without glands and 45–60 lm thick, but soon after the proboscis pore closes the epithelium becomes more sparsely ciliated and contains gland cells that are histologically identical with those making up the frontal gland lobules. In the more posterior parts of the rhynchodaeum these lightly basophilic glands are predominantly confined to the dorsal half of the epithelium. Occasional small, scattered acidophilic glands are also evident in the posterior rhynchodaeal epithelium. The proboscis insertion is situated in the brain region, behind the ventral cerebral commissure. A pair of nerves, one arising from the inner margin of each ventral cerebral ganglion close behind the ventral commissure, provides the origin of the proboscis nerve supply. The rhynchocoel does not reach the posterior half of the body. Its wall contains only a circular muscle layer which, in places, is up to 90 lm or more thick (Fig. 22). The muscle fibres, particularly in the foregut region, are loosely arranged in contrast to the intestinal region where they are more compact and the muscle layer is reduced to a thickness of about 45–50 lm. The connective tissue basement layer encircling the rhynchocoel is anteriorly 15 lm across, posteriorly only about 2–3 lm. The width of the rhynchocoel relative to the body diameter varies; above the mouth it is only about 10% of the body diameter, but behind the mouth rapidly increases to some 35% and, posterior to the level of the rhynchocoelic bodies, is mostly 50% or more of the body width. The proboscis is regionally differentiated. Its anterior portion, some 400–425 lm in overall diameter when retracted, comprises an epithelium 30–45 lm tall which contains few gland cells and is developed into four distinct longitudinal ‘welts’ of tissue. The two distinct proboscis nerves, which are about 60 lm in maximum dimension, are situated on opposite sides of the organ between the epithelial basement membrane and the proboscis musculature; they tend to protrude distally and so distort the epithelium towards the proboscis lumen. Below both the epithelium and the nerves a connective tissue layer intervenes before the longitudinal musculature, which is up to about 90 lm thick and is followed in turn by a thick inner connective tissue layer and a flattened inner lining. No circular muscles can be distinguished in this portion of the proboscis. For most of its length, in contrast, the proboscis is about 500 lm in diameter and composed of a glandular epithelium 65–70 lm tall, a thin outer connective tissue layer, an outer circular muscle coat 15–25 lm wide, an inner longitudinal muscle layer about 70 lm in maximum thickness, an inner connective tissue zone and a lining layer (Fig. 22). No rhabditoid glands could be found in the proboscis epithelium. In the posterior region of the
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proboscis, 550–600 lm in maximum diameter, the epithelium is reduced to a height of only 15–45 lm and contains fewer glands, the two nerves are very much flattened, smaller and less distinct, the longitudinal musculature has a maximum width of only 40–45 lm and the inner connective tissue zone, though remaining distinct, is very thin. Alimentary canal. The small mouth opens below the rear of the brain. The foregut epithelium, up to about 60 lm thick, is dominated by basophilic gland cells and, except on its dorsal margin, tends to be deeply folded (Fig. 22). The density of the glands gradually decreases posteriorly. The foregut nerve supply is well developed; it consists of 10–17 nerves arranged in a plexus, running either immediately outside the foregut epithelial basement membrane in the parenchyma or, more commonly, between the basal region of the epithelial cells and their basement membrane. The nerves can be distinguished on all sides of the foregut. The junction between foregut and intestine is marked by a change in gland cell type and density and by the more sparsely distributed cilia of the gastrodermis. The intestinal epithelium is not folded, has a thickness of 90–150 lm and lacks lateral diverticula. Blood system. In the anterior part of the head a pair of spacious lateral lacunae connect above the rhynchodaeum by an equally spacious transverse connective. Both the lateral lacunae are irregularly subdivided by muscle and connective tissue fibrils. The cephalic lacunar network extends throughout the head region but, farther back where the rhynchodaeum is dorsoventrally extended, the dorsal portions of the network are missing. The cephalic lacunae remain spacious as they pass through the brain region (Fig. 23), behind the proboscis insertion expanding to almost completely surround the anterior portion of the rhynchocoel except where the buccal wall protrudes from the ventral margin. In the oral region the two large lateral lacunae are irregularly crossed by connective tissue and muscle strands, but towards the rear of the mouth begin to become increasingly subdivided to form a plexus of smaller channels which extend back along the lateral and ventral margins of the foregut (Fig. 22). The branches of the plexus run in the parenchyma between the body wall longitudinal and inner circular muscle layers. On each side of the body the most dorsal channel, often close to the lateral wall of the rhynchocoel, remains consistently larger than and often fuses with other branches of the plexus. In the more posterior part of the foregut the plexus becomes reduced in complexity, and the branches are both smaller in size and tend to have thicker walls. In several places throughout the length of the foregut vascular plexus, slender canals lead off from the most dorsal channel on each side, pass through the rhynchocoel muscle layer and penetrate the lateral rhynchocoel wall to lead to the two rhynchocoel bodies (Fig. 22). These are exceptionally long, extending back in the rhynchocoel wall for some 3.9 mm and reaching into the intestinal region of the body. The length of these rhynchocoel bodies far exceeds that reported for any other species of Tubulanus and their arrangement is more like the rhynchocoelic villus described from many heteronemerteans. They have a multicellular, acidophilic appearance and are mostly somewhat triangular in shape, their distal surface being distinctly flattened. Their form varies; in some sections the rhynchocoel bodies are up to 110 lm wide but only about 15–20 lm in height, whereas in others they are 80–90 lm tall but only 60–75 lm wide. Finely granular acidophilic material distinguishable in the vessels extending through the rhynchocoel bodies can also be
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seen in the canals leading between the blind-ending bodies and the dorsal branches of the foregut vascular plexus. The arrangement of the blood supply in the intestinal region is similar to that described above for Tubulanus hylbomi sp. nov. Nervous system. The large and well developed cerebral ganglia (Fig. 23) possess an outer, but no inner, neurilemma. As in Tubulanus hylbomi sp. nov., bundles of longitudinal muscle fibres run between the epidermal basement layer and the lateral and ventrolateral margins of the brain (Fig. 23), but do not extend below the ventral cerebral commissure. The body wall outer circular muscle layer, although extending alongside the lateral cerebral borders, is also missing ventrally. The ventral commissure is about 115 lm thick, whereas the single dorsal commissure, which crosses the body above the anterior oral region, is only 40–46 lm wide. No evidence of neurochord cells could be distinguished in any part of the brain. The neural layer in the head is well developed. It consists of large numbers of distinct nerves that are very variable in size but with a maximum dimension of some 75 lm. Several other stout nerves can be distinguished. The proboscis nerves emerge from the inner surface of the ventral cerebral ganglia and enter the proboscis insertion through its ventrolateral margin. A pair of large nerves, in places 130–140 lm wide, leads back from the ventral brain lobes to form the buccal nerve supply. The buccal nerves are transversely joined by a slender commissure above the front of the mouth, then pass on either side of the mouth before branching to form the foregut nerve plexus. There is only a single dorsal nerve, up to 60 lm in diameter, running between the body wall outer circular muscle layer and the epidermal basement layer (Fig. 22). Each of the cerebral sensory organs is, as in Tubulanus hylbomi sp. nov., served by dorsal and ventral nerves but in the present species these lead separately from the respective brain lobes, rather than branching from a single nerve. Sensory organs. The present species does not possess eyes, and no trace of the lateral sensory organs reported in some species of Tubulanus could be distinguished. The cerebral sensory organs are situated in the basal portion of the epidermis, between the dorsal and ventral cerebral ganglia, towards the rear of the brain region. They have a maximum diameter of about 150 lm and extend back for some 240 lm. The ciliated cerebral canal, in which both major and minor ciliated canals are easily distinguishable, open laterally in front of the cerebral organs to enter them through their anterior margins. The canals continue directly backwards but, near the posterior limits of the cerebral organs, turn transversely to form a chamber some 45 lm across. The canals are surrounded by neuroganglionic tissues which are in turn almost completely enclosed by gland cells; the latter also extend into the adjacent epidermal tissues. As in Tubulanus hylbomi sp. nov., there are two cerebral organ nerves, but in the present form dorsal and ventral nerves entering each cerebral organ emanate from the respective cerebral ganglia, rather than from a single nerve which then forks. Frontal glands and apical organ. The apical organ forms a long tubular chamber, 90 lm or more in diameter, opening into the front of the proboscis pore epithelium. It extends posteriorly for a short distance above the rhynchodaeal epithelium. The frontal glands are extensive and possess a typical lobular arrangement, although they are not as abundant as in Tubulanus hylbomi sp. nov. The glands extend
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back to the anterior brain region but do not, as in Tubulanus hylbomi sp. nov., reach the proboscis insertion. Excretory system. The nephridial tubules, situated in the anterior intestinal region of the body, run in the parenchyma above the lateral blood vessels outside the body wall inner circular muscle layer. No evidence of an anterior gland-like region to the excretory system, as described for some species of Tubulanus, could be distinguished. The excretory tubules discharge via a single nephridiopore on either side of the body. Reproductive system. The gonads are distributed in bundled groups along the lateral margins of the body. The sexes are separate and were mature at the time of collection (April). Systematic discussion. Sundberg & Hylbom (1994: fig. 9) showed that two of the palaeonemertean species included in their phylogenetic analyses, HK sp. 5 (described above as Tubulanus hylbomi sp. nov.) and HK sp. 6 (the present taxon) are closely related, although certain morphological differences can be distinguished between them (ibid.: table 2). In their figure 12 both of these Hong Kong tubulanids, together with nine previously described species, form a discrete clade (Sundberg & Hylbom, 1994) and the present form can clearly be included in this genus. The colour pattern of HK sp. 6 differs from that of each of these nine taxa (Table 2) as well as from that described above for Tubulanus hylbomi sp. nov., but one unique anatomical feature of the form, regarded as a synapomorphy for the taxon, is the unusual length of the rhynchocoel bodies; this is far greater than reported for any other species of palaeonemertean. Other features also enable the present species to be distinguished from other members of the clade; for example, all the species except for Tubulanus capistratus, Tubulanus floridanus and Tubulanus hylbomi sp. nov. possess muscle crosses between their body wall inner and outer circular muscle layers (Sundberg & Hylbom, 1994: table 1, Character 11), and whereas the present form has only a single, upper, median dorsal nerve (Sundberg & Hylbom, 1994: table 1, Character 27), Tubulanus annulatus, Tubulanus nothus, Tubulanus polymorphus, Tubulanus rubicundus, Tubulanus superbus and Tubulanus theeli each possess both upper and lower dorsal nerves. It is thus concluded that the present taxon is a new species, for which the name Tubulanus longivasculus is proposed.
KEY TO THE PALAEONEMERTEANS OF HONG KONG
The following key, primarily based upon features distinguishable in the living nemerteans, is intended for field use. Some of the species, however, cannot be reliably separated by their external characters alone; for these taxa internal distinguishing features that can only be determined through the use of histological methods are provided in italics within parentheses. 1. 1a.
With distinctive colour pattern consisting of longitudinal stripes, with or without transverse bands ...............................................................................2 Without colour pattern, body more or less uniformly coloured throughout, although tip of head or anterior region may be suffused with darker pigmentation than remainder of body ..........................................................5
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3.
3a.
4.
4a. 5. 5a.
6. 6a.
7. 7a.
8. 8a.
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Colour pattern consisting of 2 or 3 longitudinal stripes, with or without transverse bands.............................................................................................3 Tip of head white, general body colour pale yellowish-white to light fawn, marked with 2 dorsal and 3 ventral light brown longitudinal stripes, the former both wider and darker than the latter; the stripes are interrupted by transverse whitish bands, first 3 bands more widely separated than remainder; head rather spatulate, marked off from body by slight constriction, with 8–10 irregularly distributed small epidermal eyes on each side .................... ................................................................... Carinesta tubulanoides Gibson, 1990 Head rounded, clearly demarcated from body; colour pattern consisting of single mid-dorsal and 2 lateroventral white longitudinal stripes or 2 pale brown dorsal stripes, with transverse bands which may be very obvious or somewhat indistinct .......................................................................................4 Head bluntly rounded, not demarcated from body; anteriorly pale olive brown on all sides, soon posteriorly separating into broad dorsal and ventral longitudinal stripes of some colour which, along lateral margins, fade to a whitish or very pale brown hue; ventral stripe about half to two-thirds width of dorsal..................................................Procephalothrix orientalis Gibson, 1990 General colour light brown with 2 white lateroventral stripes which anteriorly extend to rear of head, and single median dorsal white stripe which almost reaches tip of head and here forms cross; with unevenly spaced white transverse bands, commencing about 2 cm behind head, extending throughout body, head with white margins and white band present immediately in front of mouth.............................................. Tubulanus hylbomi sp. nov. General colour brown, paler ventrally, with 2 distinct dorsal pale brown longitudinal stripes, lateral body margins whitish, with indistinct whitish transverse bands..................................Tubulanus longivasculus sp. nov. Without eyes ..................................................................................................6 Bluntly pointed head on either side with distinct row of up to about 20 eyes extending from tip of snout back to brain region; general colour opaque to translucent white, sometimes with very pale pink tinge posteriorly .............. ................................................ Cephalotrichella alba Gibson & Sundberg, 1992 General colour an opaque to translucent white; mouth ventral, indistinct 7 Mouth ventral, large and distinct, located some distance behind anterior tip; colour variable, ranging from an overall pale translucent yellowish in smaller individuals to a general bright orange in large specimens; in smaller examples tip of head often distinctly orange, this colour sometimes extending back into trunk region before fading to yellowish; sexually mature specimens almost entirely orange with gonads appearing as whitish patches along lateral margins .......................................Procephalothrix arenarius Gibson, 1990 (Brain and longitudinal nerve cords situated between epidermal basement layer and body wall outer circular muscle layer) ...........................................................................8 (Brain and longitudinal nerve cords situated in proximal region of epidermis; cerebral sensory organs present; body wall musculature comprising outer circular and inner longitudinal layers, but with inner circular layer present in foregut region; blood system without mid-dorsal vessel)...................................... Carinina sinensis sp. nov. (With cerebral sensory organs; mid-dorsal blood vessel present; body wall musculature comprising outer circular and inner longitudinal layers)............................................9 (Without cerebral sensory organs; mid-dorsal blood vessel absent; body wall musculature
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9. 9a.
10. 10a.
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comprising outer circular, middle longitudinal and inner circular layers)....................10 (Blood system in foregut region with lateral vessels developed into vascular plexus; middorsal blood vessel penetrating rhynchocoel to form rhynchocoelic villus; brain lobes transversely linked by 2 dorsal commissures).............Hubrechtella alba Gibson, 1997 (Blood system in foregut region consisting of two lateral vessels which do not form a vascular plexus; mid-dorsal blood vessel not forming a rhynchocoelic villus; brain lobes transversely linked by 1 dorsal commissure) ................................................................ ............................................................. Hubrechtella sinimarinus sp. nov. (Posterior end of rhynchocoel with massive muscular sac formed from circular muscle fibres; proboscis with complex construction, with several histologicall distinct regions)............... .....................................................................Callinera bergendali sp. nov. (Posterior end of rhynchocoel without muscular sac; proboscis simple, with more or less uniform construction throughout its length)................................................................ ...................................................... Parahubrechtia jillae gen. et sp. nov.
ACKNOWLEDGEMENTS
PS wishes to thank Professor Brian Morton for inviting him to participate in the Fourth International Marine Biological Workshop, held in Hong Kong during April 1989, during which time the palaeonemerteans described in this paper were collected. Financial support for the study, provided to PS by the Swedish Natural Science Research Council, is gratefully acknowledged. Our thanks are also due to Professor ‘Pete’ Riser, Dr Jon Norenburg and Dr Alex Rogers for commenting on the original manuscript.
REFERENCES
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