A new freshwater mite of the marine genus Halacarellus (Acari: Halacaridae) from the Austrian Alps (Styria, Gesäuse National Park): Description and reflections on its origin

Zoologischer Anzeiger 250 (2011) 151–159

A new freshwater mite of the marine genus Halacarellus (Acari: Halacaridae) from the Austrian Alps (Styria, Gesäuse National Park): Description and reflections on its origin Ilse Bartscha,b,∗ , Reinhard Gereckea,b a b

Forschungsinstitut Senckenberg, c/o DESY, Notkestr. 85, 22607 Hamburg, Germany Biesinger Straße 11, 72070 Tübingen, Germany

Received 19 October 2010; received in revised form 9 February 2011; accepted 12 February 2011 Corresponding editor: S. De Grave

Abstract A new halacarid species, Halacarellus fontinalis n. sp., from a spring in the Gesäuse National Park, Austria is described. The species is characterized by three pairs of large, equal-sized acetabula and slender claws and is expected to have evolved in the Tertiary from a Tethyan-Paratethyan Halacarellus species. Caspihalacarus Viets, 1928, with a single species, C. hyrcanus Viets, 1928, has large and external acetabula similar to those in H. fontinalis. Caspihalacarus is synonymized with Halacarellus. © 2011 Elsevier GmbH. All rights reserved. Keywords: Halacaroidea; Halacarellus; Caspihalacarus; Fresh water; Paratethys

1. Introduction Halacarid mites are exclusively benthic and primarily marine, but amongst the more than 1000 species at present described, more than 50, in less than 20 genera, are specialized for a life in continental and coastal fresh and oligohaline brackish water habitats (Bartsch, 2009). Freshwater halacarid mites are found both in subterranean and in surface waters, in slightly brackish as well as in humic waters. The freshwater halacarid mites represent a heterogeneous group, their ancestors have colonized fresh water in various epochs, from the Mesozoic or even Pre-Mesozoic onwards (Bartsch, 1996), and a migration from marine to fresh, as well as vice versa, is expected to go on (Bartsch, 2008). At present 26 species, in 14 genera, have been recorded from European waters (Bartsch, 2006). Species with records ∗ Corresponding author at: Forschungsinstitut Senckenberg, c/o DESY, Notkestr. 85, 22607 Hamburg, Germany. E-mail address: [email protected] (I. Bartsch).

0044-5231/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.jcz.2011.02.003

from Austria are Caspihalacarus hyrcanus Viets, 1928, Lobohalacarus weberi (Romijn and Viets, 1924), Porohalacarus alpinus (Thor, 1910), Porolohmannella violacea (Kramer, 1879), Soldanellonyx chappuisi Walter, 1917, and S. monardi Walter, 1919 (Viets, 1956; Bartsch and Panesar, 2000).

2. Materials and methods The Gesäuse National Park, Austria, includes diverse habitats such as rock, woodland and alpine grassland and is rich in springs (Haseke, 2005a,b). In the course of four “fountain weeks”, specialists from several European countries met in the years 2007–2010 in order to contribute to a survey of the spring fauna of this area. Amongst the aquatic mite fauna, Soldanellonyx chappuisi was the halacarid most commonly found, being present in about one-third of the springs studied and in numbers contributing with about 3% (Gerecke, 2011).

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The new Halacarellus species was found in a rheocrene spring complex, consisting of several outflows arranged along a vertical transect, from a thin spruce forest to an Alpine meadow which is used by cattle. Between the uppermost and the lowermost spring mouths, an area of unstable flow is developed. After long periods of drought, flow may be interrupted also in the meadow part, though leaving some remnant humid areas where a few resistant species may survive. The composition of the fauna reflects the flow conditions; oligochaetes and chironomid larvae are dominant in all parts, but plecopteran, trichopteran and simuliid dipteran larvae are restricted to the lower part. All over density of chironomids and plecopterans is increasing from the upper to the lower part. The amphipod Niphargus aggtelekiensis Dudich, 1932 (see Fiˇser et al., 2010) was found in large populations both in the upper and in the lower, but not in the middle part. The halacarids described here were found in the lower spring mouth. Samples were taken and treated as described in detail by Franz et al. (2006). The mites were cleared in lactic acid and mounted in glycerine jelly. Slides with the holotype and paratype are deposited in the Zoological Museum of the University Hamburg, Hamburg (ZMH). Abbreviations used in the descriptive part: AD, anterior dorsal plate; AE, anterior epimeral plate; ds-1 to ds-6, first to sixth pair of dorsal idiosomatic setae, numbered from anterior to posterior; GA, genitoanal plate; GO, genital opening; OC, ocular plate(s); P-2 to P-4, second to fourth palpal segment; pas, parambulacral seta(e); PD, posterior dorsal plate; PE, posterior epimeral plate(s); pgs, perigenital seta(e). The legs are numbered from I to IV, their segments from 1 to 6 (from basal to apical). Drawings were prepared using a drawing tube.

3. Genus Halacarellus Viets, 1927: Halacarellus fontinalis n. sp. 3.1. Material Holotype female, ZMH A1/11, Austria, Gesäuse National Park, Pfarreralm, 47◦ 23 N, 14◦ 24 E, 1308 m, 17.07.2007, coll. R. Gerecke. Paratype deutonymph, ZMH A2/11, same site as holotype, 07.06.2010. coll. R. Gerecke.

3.2. Diagnosis Length of idiosoma 350 ␮m. With pair of large platelets between AD and OC. Ocular plate with small seta in anterolateral corner. PE with three ventral setae. Female GA with three pairs of large, equal-sized external acetabula. Each acetabulum surrounded by slender papillae. Leg I wider than following legs. Telofemur I with two to three ventral setae and tibia I ventrally with four spur-like and three bristle-like

setae. Paired claws slender, claws of tarsi II to IV with few delicate tines in concave part.

3.3. Etymology The species name is derived from fons, fontis (Latin), a spring.

3.4. Description Female: Idiosoma flattened, anterior margin truncate, its colour pale; eye pigment lacking. Length 350 ␮m, width 190 ␮m. Dorsum with large dorsal plates and pair of platelets (Fig. 1A). Ornamentation of plates very delicate, marginal areas of AD and PD with faint reticulation. Length of rectangular AD 92 ␮m, width 100 ␮m; anterior margin truncate. Length of OC 70 ␮m, width 43 ␮m. Cornea lacking. A small seta in anterolateral angle of OC (Fig. 1A, s), canaliculus near posterior end. Length of PD 230 ␮m, width 127 ␮m. Rather large pair of platelets between OC and AD, their size 30 × 50 ␮m. Small sclerites between PD and PE just anterior to level of insertion of leg IV. One pair of small gland pores on AD. Dorsal setae tiny; pairs of ds-1 on AD at about 0.5 relative to length of AD (seta in right half absent in holotype). Pairs of ds-2, ds-3 and ds-4 on minute sclerites in striated integument; ds-2 between AD and OC, ds-3 between OC and PD, ds-4 between PD and PE; pair of ds-5 in margin of PD level with insertion of leg IV, ds-6 in posterior margin of PD Ventral plates marginally with very slight foveate ornamentation, ventrally almost smooth. Length of AE 132 ␮m, width 182 ␮m, with three pairs of setae (one seta lacking in holotype) (Fig. 1B). Length of PE 145 ␮m; each plate with one dorsal and three ventral setae. Length of GA 151 ␮m, width 125 ␮m. GA with two pairs of pgs. Length of GO 72 ␮m, width 57 ␮m. All three pairs of acetabula external, equal-sized, 9–10 ␮m in diameter. Each acetabulum surrounded by 13–14 slender papillae. Papillae up to 4 ␮m long. Genital sclerites with two pairs of tiny subgenital setae, one pair near anterior margin, one pair at about level of anteriormost pair of acetabula. Basal pair of genital spines spur-like, visible through genital sclerites (Fig. 1H, gsp); one pair of slender genital spines protruding. Ovipositor in rest extending beyond GO to level of anterior pair of pgs, not reaching anterior margin of GA. Length of gnathosoma 100 ␮m, width 68 ␮m. Tectum truncate. Rostrum triangular in ventral aspect, its length 45 ␮m, not reaching beyond P-2. Rostrum with two pairs of maxillary setae and two pairs of small rostral setae (Fig. 1C). Rostral sulcus extending halfway between pairs of maxillary setae. P-2 with one seta, P-3 medially with short spur-like seta. P-4 with three setae in basal whorl (Fig. 1D). Leg I wider than following legs (Fig. 2A–D). Integument of legs without marked ornamentation. Telofemora I and II slightly longer than tibiae of these legs, telofemora III and IV shorter than tibiae. Telofemur I 2.3 times longer than

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Fig. 1. (A)–(H). Halacarellus fontinalis n. sp., female; (A) idiosoma, dorsal; (B) idiosoma, ventral; (C) gnathosoma, ventral; (D) gnathosoma, lateral; (E) tip of tarsus I, lateral (medial setae and claw omitted); (F) tip of tarsus II, medial (lateral setae and fossary setae in broken line; paired claws omitted); (G) tip of tarsus III, medial (lateral setae and claw in broken line); (H) genital opening, ventral. (ca, canaliculus; ac, acetabulum; glp, gland pore; gsp, genital spine; pgs, perigenital seta; s, seta; so, solenidion) Scale = 50 ␮m.

high, telofemora II to IV 2.6–2.7 times. Leg chaetotaxy from trochanter to tibia: leg I, 1, 2, 6–7, 7, 10; leg II, 1, 2, 4, 4, 7–8; leg III, 1, 2, 3, 3, 5; leg IV, 0, 2, 3, 3, 5. Telofemur I with two to three ventral setae, following telofemora each with one slender ventral seta. Tibia I with seven ventral setae, four of them spur-like and three bristle-like (Fig. 2A). Tibia II with three dorsal setae, one slender ventrolateral seta and two to three bristle-like ventromedial setae, anteriormost of the latter setae pectinate (Fig. 2B). Tibiae III and IV with pair of ventral setae. All tarsi with fossa membranes. Tarsus I dorsally with three setae and a solenidion, 7 ␮m long, inserted on lateral fossa membrane, ventrally with spine and two minute setae, and apically with pair of pas doublets. Famulus within enlarged lateral fossa membrane (Fig. 1E). Tarsus II with three dorsal setae; solenidion on medial fossa membrane 9 ␮m long (Fig. 1F); tip of tarsus II with pair of pas singlets. Tarsi III (Fig. 1G) and IV each with three dorsal setae and apical pair of pas. Paired claws long and slender. Claws on tarsus I smooth, those on following tarsi with about 12 delicate, up to 2 ␮m long tines (Fig. 1G). Paired claws without accessory process. On tarsus I central sclerite with small claw. Central sclerites on following tarsi small, without claw-like process. Deutonymph: Length 297 ␮m. Dorsal plates slightly smaller than in female. Size of dorsal platelets 22 × 15 ␮m. Arrangement of dorsal idiosomatic setae and pores as in female and OC with minute seta in anterolateral corner (Fig. 2

E). AE and PE with three pairs of ventral setae. GA with two pairs of acetabula, each about 8 ␮m in diameter and surrounded by 12–14 short tooth-like papillae (Fig. 2G). Leg chaetotaxy from trochanter to tibia: leg I, 1, 2, 5, 5, 9; leg II, 1, 2, 4, 4, 5–6; legs III and IV, 1, 2, 3, 3, 5. Telofemur and genu I each with 2/3 ventral/dorsal setae. Telofemur II with 1/1/2 ventral/lateral/dorsal setae, telofemora III and IV with 1/2 ventral/dorsal setae. Tibia I ventromedially with one slender and two spur-like setae, ventrolaterally with one slender and one spur-like seta, dorsally with four setae. Tibia II with one to two ventromedial bristle-like setae and one slender ventrolateral seta; dorsally with three setae. Tibiae III and IV each with three dorsal and a pair of ventral setae. In contrast to female, trochanter IV with a ventral seta (Fig. 2F).

3.5. Remarks The female Halacarellus fontinalis has three pairs of conspicuously enlarged external acetabula whereas Halacarellus species in general have three pairs of small acetabula inside the genital opening, covered by the genital sclerites, accordingly in an internal position. Another unique character is the small seta in the anterolateral margin of the OC, in this position the other Halacarellus species bear a distinct or vestigial gland pore. An unusual character of H. fontinalis is the presence of a seta on the deutonymphal trochanter IV, but absence

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Fig. 2. (A)–(G) Halacarellus fontinalis n. sp., (A) leg I, medial, female; (B) leg II, medial, female; (C) leg III, medial, female; (D) leg IV, medial, female; (E) idiosoma, dorsal, deutonymph; (F) leg IV, lateral, deutonymph; (G) idiosoma, ventral, deutonymph. Scale = 50 ␮m.

of that seta in the female. Apart from very few exceptions (e.g. in Acanthohalacarus Bartsch, 2001), there is no change in the number of setae of the trochanters from the last nymphal stage to the adult halacarid (Bartsch, 1998b, 2003, 2007). Within the family Halacaridae, there is no record of any reduction of setae from one to the following stage. More material of H. fontinalis may prove this character (seta absent or present) to vary in both adults and nymphs. Most conspicuous in the female H. fontinalis are the enlarged external acetabula. Such acetabula are also present in Caspihalacarus hyrcanus, a species spread in brackish and freshwater areas of the Caspian and Black Sea and in rivers emptying into these basins; recently C. hyrcanus was taken in the Rhine (Bij de Vaate et al., 2002; Martens et al., 2006; Bartsch, 2006). Differences between H. fontinalis and C. hyrcanus are in the: (1) size (350 ␮m versus 450–540 ␮m); (2) arrangement and shape of the dorsal plates and platelets (PD 1.8 times longer than wide and a pair of large platelets present between AD and OC versus PD only slightly, 1.0–1.1 times, longer than wide and all platelets small); (3) cornea and eye pigment (both lacking versus intensely coloured eye spot and OC with cornea); (4) seta on the OC (with minute seta in anterolateral corner versus a gland pore in that position); (5)

number of setae on the PE (three ventral setae versus two); (6) size of the ovipositor (extending beyond the level of the anterior pair of pgs but far from reaching the anterior margin of GA versus extending to the anterior margin of GA); (7) shape of the female acetabula (all three acetabula almost similar in size and surrounded by tiny, slender papillae versus acetabula unequal in size, anterior pair smallest, and margin of acetabula almost smooth); (8) chaetotaxy of the legs (telofemur I with two to three ventral setae, genu and tibia I with two and three and a half pairs of ventral setae, respectively, versus telofemur I with one ventral setae, genu and tibia I with one and a half and three pairs of ventral setae); and (9) shape of the claws (long and slender, tines on claws II to IV delicate versus not conspicuously slender and all tarsi with distinct tines). Troglohalacarus dentipes Viets, 1937, collected in northern Spain, in the Cueva de Aitzquirri, near Onnate, province of Guipuzcoa (Viets, 1937), is another species with three pairs of enlarged acetabula within or near the GO (Viets, 1937; Bartsch, 1989b). The shape of the plates in the single female available is obscured due to body content and ruptures in the integument. Troglohalacarus dentipes is smaller than H. fontinalis (length of female 280 ␮m versus 350 ␮m) and the

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size and arrangement of the ventral setae on telofemur I is different (two short ventral spurs versus two to three bristle-like setae).

3.6. Biology Because of the absence of cornea and eye pigment, flattened idiosoma, large plates and platelets on the dorsum with only narrow areas of striated integument between, and slender claws, this species is expected to have a hypogean life style, inhabiting a system of crevices, e.g. unsorted sediment.

4. Discussion 4.1. Possible origin of Halacarellus fontinalis Halacarellus fontinalis has strikingly enlarged acetabula and they are in an external position. The acetabula are ionpermeable areas and in species living in fresh water obviously involved in osmoregulation (Bartsch, 1973, 1974; Alberti, 1979; Alberti and Bader, 1990). The species may have evolved in the Tertiary. The collecting site of H. fontinalis is from an area which once was covered by the Tethys (Adams, 1981; Gebhardt et al., 2010). In the Miocene, about 25 million years ago, the northern part, the Paratethys, was slowly separated from the western part, the Proto-Mediterranean, and due to the rise of the Alps, rivers of central and eastern Europe emptied into the Paratethys which led to a salinity decrease (Adams, 1981). In the Late Mio- and Pliocene the Paratethys was a system of fresh and brackish water lakes and channels which covered large areas of south-eastern Europe (Fink, 1966; Adams, 1981). Representatives of the marine genera Copidognathus Trouessart, 1888, Halacarellus and Lohmannella Trouessart, 1901 obviously survived the refreshing of their environment due to an increase in size and an external position of the acetabula (Halacarellus, Lohmannella) or increase of the epimeral pores (Copidognathus). The three freshwater Lohmannella species with external acetabula, L. andrei (Angelier, 1951), L. cvetkovi (Petrova, 1965) and L. curvimandibulata (Petrova, 1969), are known from the Pyrenees (France) and northern, middle and southern Bulgaria (districts Haskovo, Rousse, Sofia Province and Tarnovo) (Angelier, 1951; Petrova, 1969; Petrova et al., 1991). Records of freshwater Copidognathus species, C. dactyloporus Benfatti, Mari & Morselli, 1989, C. hephaestios Benfatti, Mari & Morselli, 1992, C. profundus (Viets, 1936), C. tectiporus (Viets, 1935), are from coastal Black Sea areas (Bulgaria, Turkey, Ukraine), the Balkan Peninsula (Croatia, Macedonia) and Italy (Bartsch, 1999, 2006). The records are from areas once being covered or adjacent to the Tethys or Paratethys. From Central Europe north of the Alps, no freshwater representative of any of the above mentioned marine genera is known; the few species living in coastal brackish or even fresh water are marine taxa.

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The genus Halacarellus is thought to be an old taxon and many of its species may have an age of 50 million years (Bartsch, 1989a), consequently it is worth to reflect whether one of the species in the present day marine fauna is closely allied to H. fontinalis. From shallow coastal marine, brackish and freshwater areas of the eastern North Atlantic twelve Halacarellus species are known (Bartsch, 2009). Morphological characters of Halacarellus species or species groups are summarized in Table 1. The table mentions two Halacarellus species groups. One is the H. subterraneus group with the species H. subterraneus Schulz, 1933 and H. phreaticus Petrova, 1972 and the north-western Atlantic H. arenarius Bartsch, 1979. Halacarellus subterraneus is spread in the eastern and western Atlantic, in the east from Spitsbergen to the Black Sea (Bartsch, 2009). Records of H. phreaticus are from the Black Sea and Mediterranean. The three species are psammobiont and all are found in coastal areas, often in oligohaline brackish or fresh water, H. phreaticus up to 120 km away from the seashore. Characters they share are (1) PE with one dorsal and three ventral setae; (2) trochanters III and IV with two and one seta, respectively, (3) telofemur I with three spiniform ventral setae. In contrast, northern Atlantic Halacarellus species in general have one dorsal and two ventral setae on the PE, no setae on trochanter IV and a single slender ventral seta on telofemur I. The other group, the H. capuzinus group, includes the Atlantic and Black Sea species Halacarellus capuzinus Lohmann, 1893, H. chersonesus Bartsch, 1998, H. discretus Bartsch, 1998, H. floridearum (Lohmann, 1889), H. procerus Viets, 1927, H. southerni Halbert, 1915, and H. subcrispus Bartsch, 1978, the Caribbean H. tropicalis Bartsch, 1984, and the northern Pacific species H. kamchatkaensis Tuzovsky, 2010 and H. psammophilus (Krantz, 1976). All are psammophilous. Many of the species are found within a wide salinity range, often at very low values, two species were taken in freshwater bodies near the sea (distance less than 50 km), H. kamchatkaensis in a crater lake in the southern end of Kamchatka and H. subcrispus in a freshwater spring on Greenland (Tuzovsky, 2010; Bartsch, 1978; Kristensen, 1977; Timm and Vvedenskaya, 2006). Characters of this species group are: (1) PE with one dorsal and two ventral setae; (2) telofemur I with a single ventral seta; (3) tibiae II to IV each mostly with three ventral setae, one slender and smooth, two (rarely one or three) blunt and bipectinate; (4) males with the three pairs of acetabula moved to the posterior end of the GO (but none of the acetabula is conspicuously enlarged). Halacarellus fontinalis shows a general affinity to H. subterraneus and H. micropectinatus Bartsch, 1972, the idiosoma is flattened and there are platelets in the dorsal striated integument, though in different position. Halacarellus fontinalis and H. subterraneus both have three ventral setae on the PE and the deutonymphs bear a seta on trochanter IV; in addition, the claws of H. fontinalis and the north-western Atlantic H. arenarius are similar. Halacarellus fontinalis and H. micropectinatus share the characters tarsus II without a ventral seta and claws slender, without an accessory process.

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Table 1. Characters and their states in Halacarellus fontinalis, H. balticus, H. micropectinatus, H. petiti, species of the H. capuzinus and H. subterraneus group and Caspihalacarus hyrcanus. —, no data available; in parentheses, rare character states; eu, eupathidia; gr., group; J-sh, tines in J-shaped arrangement; mid, in middle part of genital opening; pas, parambulacral setae; PE, posterior epimeral; pgs, perigenital setae; post, in posterior part of genital opening; red, reduced; sgs, subgenital setae; sp, spine; vl/vm, ventrolateral/ventromedial. H. fontinalis n. sp.

H. balticus (Lohmann; 1889)

H. capuzinus gr.

H. micropectinatus Bartsch, 1972

H. petiti (Angelier, 1950)

H. subterraneus gr.

C. hyrcanus Viets, 1928

Number of pairs of platelets (>4 ␮m wide) PE, number of ventral setae Female, pairs of pgs Female, pairs of sgs Male, pairs of sgs Female, number of genital acetabula Female, position of genital acetabula Female, size of genital acetabula Male, number of genital acetabula Male, position of genital acetabula Male, position of genital acetabula III-1, number of setae IV-1, number of setae I-3, number of ventral/dorsal setae II-3, number of ventral/dorsal setae III-3, number of ventral/dorsal setae IV-3, number of ventral/dorsal setae I-4, number of ventral/dorsal setae II-5, number of ventrolateral setae II-5, number of ventromedial setae III-5, number of vl/vm setae IV-5, number of vl/vm setae I-6, apex, number of ventral setae (pas excluded) II-6, apex, number of ventral setae (pas excluded) Pectines Accessory process

1

0

0

3

3

0–1

1

3 2 2 — 3 external 9–10 — — — 1 0(–1) 2–3/4 1/3 1/2 1/2 4/3 1 3 1/1 1/1 2eu

2 2 2 5–7 3 internal 5–8 3 internal 2 mid, 1 post 2 0 1/5 1/4–5 1/4 1/4 2/3 3 3 1/1 1/1 2eu

2 2 2 5(–6) 3 internal 3–7 3 internal 3 post 1 0 (0–)1(–2)/3(–4) (0–)1/3 0/2 0/2 2/3 1 (1–)2 1/2–3 1/2 2eu

2 2 2 5 3 internal 5 3 internal 3 post 2 0 1/5–6 1/5–6 1/3–5 1/4 2/3 3 3 1–2/1 1/1 2eu

2 2 2 5–6 3 internal 6–7 3 internal 2 mid, 1 post 2 0 1/5 1/(4–)5 1/3 1/3 3–5/3 3 3 1/1 1/1 2eu

3 2 2 5 3 internal 3–9 3 internal 3 post 2 1 3/4–6 1–2/3–5 1–3/3–4 1–2/3 2/3 1–3 2–3 1–2/1–3 1–2/1–3 2eu

2 2 2 5 3 external 8–20 3 external 1 mid, 2 post 2 0 1/5–7 1/5–6 1/2 1/3 3/3 1 3 1/1 1/1 (3–)4eu

0

1

0

0

1

1

2(–3)

red absent

J-sh present

J-sh present

red absent

J-sh present

J-sh to red present to absent

J-sh present

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Species

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The latter species, H. micropectinatus, is known from sandy Black Sea beaches and north-eastern Atlantic salt marshes (France, The Netherlands, Germany) (Bartsch, 1972, 1976b, 1998a). The detection of a new halacarid species in Central Europe, a relatively well-documented part of the world, is out of the ordinary routine. The type locality is located in an area largely spared from glaciation during the last (Würm) ice age (Van Husen, 1987; Frisch et al., 2002). There is a high frequency of endemic plant species in this area (Rabitsch and Essl, 2009), and several groundwater- and spring-dwelling taxa, taken in the Gesäuse, are un-recorded from other parts of the Alpine chain (cf. Haase et al., 2000; Fiˇser et al., 2010).

4.2. Taxonomic state of Caspihalacarus The genus Caspihalacarus was erected by Viets (1928) to contain the brackish and freshwater inhabiting C. hyrcanus. According to the diagnosis (Viets, 1928), the genus is similar to Halacarellus, the only character which separates it from Halacarellus is, the acetabula are external and enlarged. Caspihalacarus hyrcanus is spread in and near rivers and lakes emptying into the Caspian and Black Sea; in the river Rhine it is expected to be a neozoan (Bij de Vaate et al., 2002; Martens et al., 2006). Caspihalacarus hyrcanus is most similar to Halacarellus petiti (Angelier, 1950), both in the life style and external characters, and in the Late Tertiary a Paratethyan population of an ancestor of the latter species may have given rise to C. hyrcanus (Bartsch, 1996). Both species, C. hyrcanus and H. petiti, are epibenthic, found in and on sediment amongst roots of vascular plants, green algae and tubes of an associated fauna (Bartsch, 1979; Martens et al., 2006). The salinity of the type locality of H. petiti is not known (Angelier, 1950), all other records are from brackish (up to 13 S‰) or almost freshwater areas (Morselli and Mari, 1979; Bartsch, 1979; Bartsch and Panesar, 2000). The species is spread in coastal waters of the Mediterranean (France, Italy), eastern Atlantic (France, UK) and Baltic (Germany, Sweden). Records of Caspihalacarus hyrcanus are from a salinity range of fresh to 12.5 ‰ (Viets, 1928; Bartsch, 2006). Characters the two species share are, genua I with more than two ventral setae and spermatopositor flanked by lateral wing-like lamellae (cf. Bartsch, 1976a, Fig. 5; Bartsch, 2006, Figs. 5 and 6d). The other shallow water northern Atlantic Halacarellus species bear a single pair of ventral setae on genu I, and wing-like lamellae flanking the spermatopositor have not been described. Caspihalacarus hyrcanus and Halacarellus fontinalis demonstrate an overall similarity in their morphological characters, both have the acetabula enlarged and in an external position. The species should be placed in the same genus, but they seem to have different Halacarellus ancestors and pathways into their present-day habitats. The ancestor of C. hyrcanus is expected to have used an epigean route whereas the ancestor of H. fontinalis has survived the refreshing in,

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and migrated along the groundwater table. If the two species were united within a genus Caspihalacarus, a polyphyletic taxon would be the result. Consequently, Caspihalacarus has to be abandoned and the only species, C. hyrcanus Viets, 1928, moved to Halacarellus as H. hyrcanus (Viets, 1928).

4.3. Some remarks on size and numbers of the acetabula Both Halacarellus fontinalis and H. hyrcanus have very large acetabula, in female H. fontinalis 9–10 ␮m in diameter, in H. hyrcanus 8–20 ␮m. The acetabula of the above mentioned marine Halacarellus species are smaller, in general distinct and about 3–8 ␮m wide. Noteworthy is that the acetabula of freshwater halacarid genera (Lobohalacarus Viets, 1939, Porohalacarus Thor, 1922, Porolohmannella Viets, 1933, Soldanellonyx Walter, 1917, Limnohalacarus Walter, 1917, Parasoldanellonyx Viets, 1929, Ropohalacarus Bartsch, 1989) are small (2–5 ␮m in diameter), though in several species the number is increased and more than three pairs are present. These genera assumedly invaded fresh water in the Mesozoic or Pre-Mesozoic (more than 100 million years ago) (Bartsch, 1996), in contrast, the two above-mentioned Halacarellus species most likely got adapted to fresh water in recent time, in the Late Tertiary, within the past 15 million years.

Acknowledgements Halacarellus fontinalis was collected during the fountain weeks 2007–2010, organized and financed by the National Park Gesäuse, Austria. This support is gratefully acknowledged. Thanks are also due to Christina Remschak and Harald Haseke for field assistance and important information on the study area.

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