Archeopyle structure in modern gymnodinialean dinoflagellate cysts

Review of Palaeobotany and Palynology, 44 (1985): 217--231 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

217

ARCHEOPYLE S T R U C T U R E I N M O D E R N G Y M N O D I N I A L E A N DINOFLAGELLATE

CYSTS

KAZUMI MATSUOKA Department of Geology, Faculty of Liberal Arts, Nagasaki University, Nagasaki 852 (Japan) (Received June 6, 1984 ; revised version accepted December 7, 1984)

ABSTRACT

Matsuoka, K., 1985. Archeopyle structure in modern gymnodinialean dinoflagellate cysts. Rev. Palaeobot. Palynol., 44: 217--231. Cysts of five species of gymnodinialean dinoflagellates are described. The aperture of excystment is morphologically different from the archeopyle as typically developed in some peridinialean dinoflagellates. Two major types were observed in these cysts, and they are described and named. The "chasmic archeopyle" shows a linear to slightly curved rupture. The "tremic archeopyle" marks a circular to nearly circular hole. The geographical distribution of these cysts around the Japanese Islands is shown. INTRODUCTION R e c e n t i n c u b a t i o n e x p e r i m e n t s o n m o d e r n dinoflagellate c y s t s h a v e b r o u g h t us m u c h v a l u a b l e i n f o r m a t i o n . T h e r e a l i z a t i o n t h a t t h e c a t e dinoflagellates can p r o d u c e acritarch-like cysts is o n e i m p o r t a n t result o f these investigations (Dale, 1977}. T h e c y s t s o f m o d e r n n a k e d ( g y m n o d i n i a l e a n ) dinoflagellates are p r o v i d e d with i n d i s t i n c t openings, t h e f u n c t i o n o f w h i c h is identical t o t h a t o f t h e a r c h e o p y l e d e v e l o p e d in t h e cysts o f t h e p e r i d i n i a l e a n dinoflagellates, n a m e l y an o p e n i n g f r o m w h i c h p r o t o p l a s m is released o n e x c y s t m e n t . Because these o p e n i n g s v a r y in m o r p h o l o g y , t h e y m a y be i m p o r t a n t c h a r a c t e r s in t h e classif i c a t i o n o f g y m n o d i n i a l e a n dinoflagellate cysts, b u t as y e t t h e y h a v e n o t b e e n n o t i c e d or discussed in a n y detail. R e c e n t o b s e r v a t i o n s a n d a l i t e r a t u r e s u r v e y h a v e led t o t h e c o n c l u s i o n t h a t the m o r p h o l o g y o f t h e s e o p e n i n g s in m a n y cases is identical w i t h t h a t o f t h e a r c h e o p y l e s o f t h e c a t e dinoflagellate cysts. T h e r e are, h o w e v e r , n e w t y p e s a n d in this p a p e r t w o n e w a r c h e o p y l e t y p e s are described, t o g e t h e r w i t h five g y m n o d i n i a l e a n dinoflagellate cysts, r e c o v e r e d f r o m surface s e d i m e n t s a r o u n d Japan.

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218 THE ARCHEOPYLE-- A BRIEF REVIEW Evitt (1963) proposed the Group Acritarcha (from the Greek ciKp~7o~ = uncertain; and &px~ = origin) for miscellaneous organic-walled microfossils that could not be attributed to the dinoflagetlates. In so doing, Evitt (1969) published criteria that serve to separate dinoflagellate cysts from other microfossils, "cyst shape, position of major projections (horns) or lesser projections (processes and septa), wall structure, a variety of features that reflect the plate pattern (paratabulation) and the character of a distinctive opening (archeopyle)" (Evitt, 1969, p.441). The "hystrichosphaerids", thecate dinoflagellate cysts with nontabular processes are especially similar to acritarchs in morphology. The presence of a distinctive archeopyle is the most important character for distinguishing the former from the latter. The definition of the archeopyle was first proposed by Evitt (1961) and was later revised to " t h e archeopyte is an excystment aperture in the wall of a dinoflagellate c y s t " (Evitt, 1967, p.6). Acritarchs also have such various openings as cryptosutures, splits, ruptures, outfolded flaps and pyloms (Lister, 1970; Loeblich and Tappan, 1969). These openings are also considered to be pores or holes, through which the protoplasm is released at germination. They differ from archeopyles in that they have an irregular shape and position, not reflecting any tabulation pattern or structure. CYSTS OF GYMNODINIALEAN DINOFLAGELLATES AND ACRITARCHS Evitt (1963) believed that the acritarchs are a polyphylethic group and probably include some dinoflagellate cysts. Wall and Dale (1968) carried out incubation experiments on the living cysts of some naked dinoflagellates, and observed that these cysts lack a distinctive archeopyle or paratabulation and that they closely resemble fossil acritarchs assignable to the Subgroups Acanthomorphidae and Herkomorphidae. Based on this evidence, Wall and Dale (1968, p.204) suggested that the possibility that archeopyles may exist outside the Peridiniales, i.e. among the modern Gymnodiniales, remains an open question. Dale (1977) reported the presence of an acritarchous cyst in the thecate species Peridinium faeroense Paulsen. This cyst appears to lack features such as any reflected tabulation and archeopyle, and is identifiable as Micrhystridium bifurcatum Williams (MS.). As seen above, several authors have considered the possibility that some dinoflagellate cysts, especially those of gymnodinialean forms, have been classified in the Group Acritarcha. NEW ARCHEOPYLE TYPES At present seven basic archeopyle types are known in dinoflagellate cysts: apical, intercalary, precingular, combination, epicystal, transapical and hypocystal.

219

Recent studies, however, using incubation experiments and the morphological investigation of m o d e m cysts, reveal that the cysts of some gymnodinialean dinoflagellates have acritarch-like openings, and that these openings are n o t accidental b u t are consistent in shape and position. T w o new types of opening are described below, chasmic type and tremic type. Types similar to these are k n o w n in some fossil acritarchs described as median ruptures and pylome type openings. If we accept the definition o f the archeopyle given by Evitt (1967), these t w o new opening types developed in the cysts of gymnodinialean dinoflagellates should be added to the basic archeopyle types.

Description o f new archeopyle types (1) Chasmic archeopyle (Fig.lD, E) Derivation o f name : Greek ×~opa = chasm. Definition: The opening is a linear to slightly curved rupture without operculum, and mainly formed at the median zone on the cyst. Length of rupture is various and ranges from one-tenth to half of the cyst diameter. Rupture line is mostly smooth, b u t rarely slightly zigzag. Remarks: An operculum is not produced, the protoplasm being released through a simple rupture. If this archeopyle is small, its optical cross-section shows a shallow V-shape. In other cases, the rupture may be well developed, with the cyst b o d y almost being cut into t w o hemispheres. The cysts belonging to two gymnodinialean dinoflagellates have this archeopyle type: Polykrikos hartmannii Zimmermann (Fig.lD) and Cocholodinium sp. (Fig.lE). Openings similar to this type are also observed in such early Paleozoic acritarchs as the genera Micrhystridium, Orthosphaeridium, and Unellium. (2) Tremic archeopyle (Fig.IA--C) Derivation o f name: Greek W~p~ = hole. Definition: The opening is circular to nearly circular in shape, sometimes with a slightly zigzag margin, and is usually formed in the polar region, i.e. probably the apical area, b u t rarely elsewhere. Margin of the opening is thickened in some cases. Remarks: This opening type, formed in the cyst of Polykrikos schwartzii Biitschili, has been recognized as an apical archeopyle by Harland (1977, 1981) and Reid (1978). The definition of an apical archeopyle given by Evitt (1967, p.16) is as follows: "The apical archeopyle includes the apex of the cyst and does not extend to the cingulum, it usually corresponds to apical thecal plates alone, b u t minor intercalary plates may be represented in some examples". The opening observed in the cyst of Polykrikos schwartzii is situated at the polar region, probably the apical area, and its margin shows a slightly zigzag line. The cyst, however, lacks any such paraplates as seen in many cysts of peridinialean dinoflagellates, and therefore the zigzag margin does n o t seem to be identical with either principal or accessory archeopyle parasutures.

220

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u Fig. 1. A--C. Examples of tremic archeopyle. A. Polykrikos kofoidii without distal extremities of ornaments, lateral view showing much deformed process-like ornaments and attached operculum. B. Polykrikos schwartzii without distal ends of network ridges, polar (probably apical) view showing somewhat zigzag margin of archeopyle. C. Gyrodinium instriatum after chemical treatment, lateral view showing nearly circular archeopyle at the polar end. D--E. Examples of chasmic archeopyle. D. Polykrikos hartmannii recovered from surface sediments, probably lateral view showing short conical processes and long fissure expanded longitudinally. E. Cocholodinium sp. after germination in incubation experiment, probably lateral view showing fin-like ornaments and large fissure developed longitudinally. All figures modified. In a n o t h e r case, the c y s t o f Gyrodinium instriatum c o m p l e t e l y lacks any p a r a t a b u l a t i o n structure, t h e r e f o r e it is unjustifiable t o regard its o p e n i n g as an apical a r c h e o p y l e sensu Evitt. The cysts o f the f o l l o w i n g g y m n o d i n i a l e a n species thus have this archeopyle t y p e : Gyrodinium instriatum ( F i g . l C ) , Polykrikos hofoidii ( F i g . l A ) and Polykrikos schwartzii (Fig.lB). T h e c y s t o f Gyrodinium resplendens s h o w n b y Dale {1983, fig.23) seems to have a tremic a r c h e o p y t e f o r m e d at the middle o f the epicyst.

221 DESCRIPTION OF SOME GYMNODINIALEAN DINOFLAGELLATE CYSTS Order GYMNODINIALES Lemmerrnann 1910 Family GYMNODINIACEAE Lankester 1885 Genus Gyrodinium Kofoid et Swezy 1921

Gyrodinium instriatum Freudenthal et Lee 1963 (Plate III, 5; Fig.lC) 1982 Cyst of Gyrodinium instriatum Freudenthal and Lee 1963; Fukuyo, pp.206--207, pl. I, figs. 1--6.

Description: Small elliptical to ovoidal cyst. Cyst wall consists of a relatively thick and transparent autophragm, without ornament. Archeopyle is tremic in t y p e with completely detached operculum, and is formed at a polar end, probably an apex. Dimensions: Cyst diameter 27--20 X 29--50 pm, diameter of archeopyle 10--12 pm, number of specimens measured 10. Remarks: The cyst filled with protoplasm is surrounded by transparent adhesive material provided with fine silicate particles and fragments of diatoms and silicoflagellates. These materials are dissolved by chemical treat~ ment. Before excystment, the cyst of Gyrodinium instriatum closely resembles the cysts of Protogonyaulax catenella, P. tamarensis and Gonyaulax verior in having an ellipsoidal cyst b o d y with a transparent adhesive material. The first differs from the other three species in possessing a tremic archeopyle and a somewhat ovoidal cyst b o d y after germination. Another cyst of this genus, Gyrodinium resplendens, also may have a tremic archeopyle, but its position is n o t in the polar region b u t rather in the middle part of the epicyst. This cyst is n o t similar to the cyst of G. instriatum and is covered with numerous nontabular processes (see Dale, 1983). Occurrence around Japan: Southern part of Harimanada (Fukuyo, 1982) and Bay of Senzaki (Fig.2). Genus Cocholodinium Schutt 1986

Cocholodinium sp. (Plate II, 4--5; Fig.lE) 1982 Cyst of Cocholodinium sp. Fukuyo, p.207, pl.II, figs.l--4.

Description: Proximate cyst, brown in color, small to intermediate in size and subspherical to ellipsoidal in shape. Cyst wall consists of t w o layers, periphragm and endophragm appressed between ornamentations. Endophragm probably thin and smooth, the periphragm raised into many fin-like ornaments. Its surface is coarsely granular. Most of these ornaments are distributed at random, b u t rarely the proximal base of these fin-like ornaments is trans-

222

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Fig.2. Geographic distribution of some gymnodinialean dinoflagellate cysts around the Japanese Archipelago. N G = Bay of Nagasaki; O M = Bay of Omura; S Z = Bay of Senzaki; H R = Lake Hiruga; S D = Lake Kamo; O G = Bay of Oga; A K = Bay of Akkeshi; H N = southern part of Harimanada. P . h . = P o l y k r i k o s h a r t m a n n i i ; P . k . = P o l y k r i k o s k o f o i d i i ; P.s. = P o l y k r i k o s schwartzii; G.i. = Gyrodinium instriatum ; C.s. = Cocholodinium sp. Data from the southern part of Harimanada given by Fukuyo (1982).

223 versely extended. Their distal extremities are rounded to slightly denticulate. Archeopyle of chasmic type, formed by a fissure running along the longitudinal axis of the cyst. Its length reaches nearly half of the cyst diameter. Dimensions: Cyst diameter 25--33 X 38--40 ~m, length of fin-like ornaments 5--7 pm, length of archeopyle ca. 20 ~m, number of specimens measured 3. Remarks: This cyst is apparently similar to Tylotopalla caelamenicutis Loeblich, a Silurian acritarch species, but differs from the latter in having a larger cyst b o d y and large, distinctive fin-like ornaments. Among the other cysts of gymnodinialean dinoflagellates, this cyst is distinguished by its characteristic fin-like ornaments and long chasmic archeopyle. Occurrence around Japan: Southern part of Harimanada (Fukuyo, 1982) and Bay of Omura (Fig.2). Family POLYKRIKACEAE Lindemann 1928 Genus Polykrikos Btitschli 1873

Polykrikos kofoidiiChatton 1914 (Plate I, 6; Plate II, 1--3, Fig.lA) 1980 Spiny resting cyst of Polykrikos kofoidi Chatton; Morey-Gains and Ruse, pp. 230-231, fig.4. 1980 "Acritarch" species; Arends and Damassa, pl. 2, figs.1--2, 12--13. 1982 Cyst type PS-I; Fukuyo, p.209, pl.IV, figs.7--9.

Description: Proximate cyst, elongate, light to pale brown in color. The cyst wall is made up of two or three layers, appressed between processes or shelflike ornaments. The smooth and relatively thin endophragm is the basal unit. The fibrous and coarsely wrinkled periphragm forms the complex processes or shelf-like ornaments, which are also strongly fibrous. Processes are hollow and short cylindrical to infundibular in shape, and distally open. Their proximal bases occasionally connect with adjacent ones. In some specimens not only the proximal bases, b u t also the shafts and distal extremities of processes connect and fuse with neighboring ones, forming a shelf-like ornament (Plate II, 3). Five rows of separated processes or shelf-like ornaments transversely surround the cyst body. Two of them are situated at the polar regions and probably indicate apical and antapical areas. The third series of rows is medianly located on the cyst. The archeopyle, basically circular in shape and of tremic t y p e with a slightly zigzag margin, is formed at a polar region, probably the apical area. The operculum is basically free, but rarely attached. Dimensions: Length o f cyst 52.5--74.9 pm, width 37.3--49.5 pm, length of processes 11.8--17.9 pm, diameter of archeopyle 18--25 pm, number of specimens measured; more than 30. Remarks: The cyst ofPolykrikos kofoidii reported by Morey-Gains and Ruse (1980) has short and separated spinous processes (but short cylindrical to tapering -- m y observation of their photographs). The specimens shown by Arends and Damassa (1980) and obtained from Japan differ from the former

224 in having longer and fibrous processes and a wide variation in ornament. This wide variation may be the result of the strongly fibrous periphragm which forms a shelf-like ornamentation. The cyst of Polykrikos schwartzii differs from the present cysts in possessing a network of ridges. It also has a wide variation in the network system, from fine to coarse reticulation (Harland, 1981). Some specimens of the cyst of Polykrikos kofoidii have an incomplete network of ridges formed by the periphragm. The presence of these forms suggests the possibility that the cysts of P. kofoidii and P. schwartzii have extreme variation in ornamentation. Occurrence around Japan: Bay of Omura, Bay of Senzaki, Lake Hiruga, Lake Kamo, Bay of Oga, Bay of Akkeshi, and Southern part of Harimanada (Fukuyo, 1982) (Fig.2).

Polykrikos hartmannii Zimmermann 1930 (Plate III, 1--4; Fig.lD) 1968 ?Resting spore of naked dinoflagellates. Wall and Dale, p.281, pl.4, fig.27. 1982 Cyst of Polykrileos hartmannii Zimmermann. Fukuyo, p.208, pl.III, fig.1--6. 1982 Cyst ofPolyterikos hartmannii Zimmermann. Matsuoka, pl.2, fig.13.

Description: Small to intermediate cyst, spherical in shape, and light to pale brown in color. Cyst wall consists of thin and granular periphragm and smooth endophragm, strongly appressed between processes. Processes are hollow, short and conical in shape, with acuminate and close distal extremities. At proximal base of processes some striations are well developed. The distribution of processes is completely nontabular. The archeopyle is a chasmic type and probably formed at the median cyst zone. Dimensions: Cyst diameter 48--60 um, ler~gth of processes 8--12/~m, length of archeopyle ca. 25 pm, number of specimens measured 10. Remarks: Spherical dinoflagellate cysts provided with many processes are known in such species as Operculodinium israelianum (Rossignol), O. centrocarpum (Deflandre et Cookson), Lingulodinium machaerophorum {Deflandre et Cookson) and Multispinula ? minuta Harland et Reid. The present cyst is especially similar to M. ? minuta in having a brown cyst body and slender acuminate processes. The cyst of P. hartmannii, however, differs from the others in possessing short conical processes with some striations at the proximal base and a characteristic chasmic archeopyle. Most specimens recovered from surface sediments are much deformed and do n o t show a completely spherical shape, because of the thin and weak cyst wall. The cyst, filled with protoplasts including a few red pigmented bodies, is usually surrounded by fine sediment particles held between processes. Occurrence around Japan: Bay of Nagasaki, Bay of Omura, Bay of Senzaki, Lake Hiruga, and southern part of Harimanada (Fukuyo, 1982) (Fig.2). Polykrikos schwartzii Bfitschli 1873 (Plate I, 1--5; Fig.lB) 1887 Umrindete Cyste. Hensen, p.80, pl.4, figs.32a, b, pl.6, figs.67--68. 1968 ?Resting spore of naked dinoflagellate. Wall and Dale, p.281, pl.4, fig.28.

225 1977 Cyst ofPolykrikos sp.1; Reid and Harland, pl.2, figs.l--3. 1977 Polykrikos cyst; Harland, pp.109--110, pl.4, figs.I--6. 1978 Resting cyst of Polyhrihos schwartzii Biitschli. Reid, p.227, pl.1, figs.l--9. 1981 Cyst of Polykrikos schwartzii Biitschli. Harland, pp.78--79, pl.1, figs.l--9, pl.2, figs.l--9, pl.3, figs.l--4, pl.4, figs.I---6, text-figs.2, 6--8. 1982 Cyst ofPolykrihos schwartzii Biitschli. Matsuoka, pl.2, fig.14. 1982 Cyst of Polykrihos hofoidii Chatton. Fukuyo, pp.208--209, pl.IV, figs.l--3.

Dimensions: Length of cyst 50.5--108.4 ~m, width of cyst 29.6--80.8 Urn, height of ornaments 6.6--10.3 pm, diameter of archeopyle 18--25 ~m; number of specimens measured: more than 50. Descriptive remarks: The morphology of this cyst was studied in detail by Harland {1981). The Japanese specimens coincide well with such previously reported morphological variations as finely and coarsely reticulate networks in the surface structure. Harland (1981) considered that the archeopyle of this cyst is apical on the basis of its position and the presence of the parasulcal-like notch. In Japanese specimens, the e x c y s t m e n t aperture is observed at the polar region, probably apical area, and apparently shows a circular shape with slightly zigzag margin (Plate I, 3a and 5). However, according to illustrations given by Harland (1981, text-fig.6) and m y observation on the Japanese specimens, the margin o f the openings does not consistently indicate paraplate boundaries as observed in peridinialean cysts; therefore, it does not appear to reflect the boundary between the apical and intercalary or precingular paraplate series. This evidence suggests that the nature of the opening in the cyst of Polyhrihos schwartzii differs from the typical apical archeopyle as developed in the cyst of peridinialean thecate species. The archeopyle of this cyst is of tremic type, formed at the polar region, probably the apical area. Occurrence around Japan: Bay of Omura, Bay of Senzaki, Lake Hiruga, Lake Kamo, Bay o f Oga and Bay o f Akkeshi (Fig.2). NOTE ON THE PARATABULATION-LIKE STRUCTURE OF COLONIAL GYMNODINIALEAN DINOFLAGELLATE CYSTS

Harland (1981) first described the paratabulation-like structure in the cyst of Polykrihos schwartzii based on observations of the arrangement of the lumina surrounded b y a network o f ridges, and generally recognized these lumina divided into a series of seven whorls as an identifiable paratabulation. Actually, in colonial gymnodinialean dinoflagellates such as P. schwartzii and P. kofoidii, the motile and cyst forms resemble each other because both are elongate organisms, b u t these two forms are functionally dissimilar. The reason for this is as follows. The motile form usually comprises two to eight, rarely sixteen zooids (or units) which independently possess transverse and longitudinal furrows provided with t w o flagella, while in the cyst form the paratabulation-like structure which consists o f five or seven ornamentation series is developed on the b o d y as a whole. These can n o t be divided into zooid-like units as observed in the motile form.

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229 PLATE I (× 600) (see p.226)

Polykrikos schwartzii Biitschli 1873 1. a. Ventral view. b. Optical cross-section of dorso-ventral view. c. Dorsal view, showing surface structure of coarse reticulate system. Loc. Lake Kamo (SD 3-1, 14.3/136.4). 2. a. Ventral view (?). b. Optical cross-section of dorso-ventral view, showing surface structure of fine reticulate system. Loc. Bay of Omura (OM 30-1, 17.4/143.5). 3. a. Apical view showing tremic archeopyle with slightly zigzag margin, b. Optical crosssection o f polar view. Loc. Bay o f Omura (OM 1-1, 15.3/129.4). 4 . Oblique apical view showing tremic archeopyle. Loc. Bay of Omura (OM 30-2, 6.5/ 128.3). 5. Slightly damaged specimen, oblique view showing tremic archeopyle. Loc. Bay of Omura (OM 30-1, 10.0/148.5). Polykrikos kofoidii Chatton 1914 6. a. Lateral view showing fibrous periphragm, b. Optical cross-section of lateral view showing infundibular and fibrous processes. Loc. Bay of Akkeshi (AK 3-2, 22.0/127.0). PLATE II (x 600) (see p.227)

Polykrikos kofoidii Chatton, 1914 1. a. Lateral view showing fibrous and coarsely wrinkled periphragm, b. Optical crosssection of lateral view showing strongly fibrous and fenestrate, and short cylindrical to infundibular processes, c. Lateral view showing somewhat deformed and reduced processes. Loc. Bay of Akkeshi (AK 2-2, 7.0/129.0). 2. a. Apical view showing tremic archeopyle (arrow). b. Optical cross-section of polar view showing short cylindrical processes. Loc. Bay of Akkeshi (AK 2-2, 6.0/128,2). 3. a. Optical cross-section of lateral view showing moderately deformed and strongly fibrous processes, b. Lateral view showing shelf-like ornaments formed by deformation and fusion of the adjacent processes. Loc. Lake Kamo (SD 3-1 20.4/125.6). Cocholodinium sp. 4. Optical cross-section showing fin-like ornaments surrounding the cyst body. Filled with protoplasts before germination. Loc. Bay of Omura (KOG 001). 5. a. Lateral view (?) showing chasmic archeopyle (arrow). b. Lateral view showing fin-like ornaments. Loc. Bay of Omura (KOG 002). PLATE III (all figures in interference contrast, x 700) (see p.228)

Polykrikos hartmannii Zimmermann, 1930 Optical cross-section showing long chasmic archeopyle (arrow) and long conical processes, b. Polar view (?) showing long conical processes provided with striations at proximal base. Loc. Bay of Senzaki (SZ 14-2 41.1/94.2). 2. a. Lateral view (?) showing granular surface of the periphragm and long conical processes, b. Lateral view showing chasmic archeopyle. Loc. Bay of Senzaki (SZ 14-2, 37.4/97.0). 3. a. Lateral view showing chasmic archeopyle in poorly preserved specimen, b. Lateral view showing p o o r preservation. Loc. Bay of Senzaki (SZ la-3 30.7/92.6). 4. Polar view showing p o o r preservation. Loc. Bay of Senzaki (SZ la-3, 31.0/92.6). Gyrodinium instriatum Freudenthal et Lee 1963 6. a. Optical cross section of lateral view showing relatively thick cyst wall, b. Lateral view showing circular tremic archeopyle. Loc. Bay of Senzaki (SZ la-3 29.7/83.9). 1. a.

230 In t h e c y s t o f P. kofoidii, the five r o w s o f processes or shelf-like o r n a m e n t s are closely similar to p a r a p l a t e series as r e c o g n i z e d in the c y s t o f peridinialean t h e c a t e species, b u t e a c h p a r a p l a t e c o m p r i s i n g t h e p a r a p l a t e - l i k e series is u n c l e a r and variable in n u m b e r and position. This c o n d i t i o n is the s a m e f o r the l u m i n a o f P. schwartzii as a l r e a d y r e p o r t e d b y H a r l a n d (1981). This evidence strongly suggests t h a t t h e p a r a t a b u l a t i o n - l i k e s t r u c t u r e s d e v e l o p e d in P. k o f o i d i i a n d P. schwartzii are n o t t r u e p a r a t a b u l a t i o n structures a n d n o t c o m p l e t e l y identical t o t h a t o f t h e c y s t o f p e r i d i n i a l e a n t h e c a t e species. T h e r e f o r e , t h e zigzag m a r g i n a r o u n d t h e t r e m i c a r c h e o p y l e o b s e r v e d in these cysts d o e s n o t s e e m t o reflect a c o n s i s t e n t p a r a t a b u l a t i o n b o u n d a r y . ACKNOWLEDGEMENT I a m m u c h i n d e b t e d t o Dr. R e x H a r l a n d , British Geological Survey, f o r his critical review o f t h e m a n u s c r i p t a n d valuable suggestions o n the c y s t m o r p h o l o g y . I wish to express m y d e e p g r a t i t u d e to Dr. Y a s u w o F u k u y o , University o f T o k y o , f o r his k i n d help c o n c e r n i n g m o t i l e dinoflagellates. This w o r k is p a r t l y s u p p o r t e d b y t h e J a p a n e s e Ministry o f E d u c a t i o n , Science and C u l t u r e ( M o n b u s h o ) u n d e r G r a n t - i n - A i d s f o r Scientific R e s e a r c h ( G r a n t no.5854058). REFERENCES Arends, R.G. and Damassa, S.P., 1980. Diatoms, silicoflagellates from Holocene sediments of Basins in the Southern California Continental Borderland. In: M.E. Field, A.H. Bouma, I.P. Colburn, R.G. Douglas and J.C. Ingle (Editors), Quaternary Depositional Environments of the Pacific Coast. Pacific, Sec., Soc. Econ. Paleontol. Mineral., Los Angeles, CA, pp.313--324. Chatton, E., 1914. Les cnidocysts du p6ridinien Polykrikos schwartzii Biitschli. Structure, fonctionnement, autog4n~se, homologies. Arch. Zool. Exper. Gener., 54: 157--194. Dale, B., 1977. New observations on Peridinium faeroense Paulsen (1905), and classification of small orthoperidinioid dinoflagellates. Br. Phycol. J., 12 : 241--253. Dale, B., 1983. Dinoflagellate resting cysts: "Benthic plankton". In: G.A. Fryxell (Editor), Survival Strategies of the Algae. Cambridge University Press, Cambridge, pp.69--136. Dodge, J.D., 1983. Marine Dinoflagellates of the British Isles. Her Majesty's Stationery Office, London, 303 pp. Evitt, W.R., 1961. Observations of the morphology of fossil dinoflagellates. Micropaleontology, 7: 385--420. Evitt, W.R., 1963. A discussion and proposals concerning fossil Dinoflagellates, Hystrichospheres and Acritarchs. Natl. Acad. Sci., Proc., 49: 158--164; 298--302. Evitt, W.R., 1967. Dinoflagellate studies, II. The archeopyle. Stanford Univ. Publ., Geol. Sci., 10(3): 1--88. Evitt, W.R., 1969. Dinoflagellates and other organisms in palynological preparations, in: R.H. Tschudy and R.A. Scott (Editor), Aspects of Palynology. John Wiley, New York, NY, pp.439--479. Evitt, W.R. and Wall, D., 1968. Dinoflagellate studies IV. Theca and cysts of recent freshwater Peridinium limbatum (Stokes) Lemmermann. Stanford Univ. Publ., Geol. Sci., 2(4): 1--15. Freudenthal, H.D. and Lee, j.j., 1963. Glenodinium halli n. sp. and Gyrodinium instrialum n. sp. Dinflagellates from New York waters. J. Protozool., 10: 1--9.

231 Fukuyo, Y., 1982. Cysts of naked dinoflagellates. In: Fundamental Studies of the Effects on the Marine Environment of the Outbreaks of Red Tides. Reports of Environmental Sciences, B 148-R14-8, Mombusho, pp.205--214 (in Japanese, with English abstract). Harland, R., 1977. Recent and late Quaternary (Flandrian and Devensian)dinoflagellate cysts from marine continental shelf sediments around the British Isles. Palaeontographica, 164B: 87--125. Harland, R., 1981. Cysts of the colonial dinoflagellate Polykrikos schwartzii Biitschli 1873 (Gymnodiniales), from Recent sediments, Firth of Forth, Scotland. Palynology, 5: 65--79. Hensen, V., 1887. lJber die Bestimmung des Planktons -- oder des im Meere treibenden Materials an Pflanzen und Thieren. Ber. Komm. Wiss. Unters. Dsch. Meere, Kiel 1882-1886, 5(1): 1--108. Lentin, J.K. and Williams, G.L., 1976. A monograph of fossil peridinioid dinoflagellate cysts. Bedford Inst. Oceanogr. Rep., BI-R-75-16: 1--237. Lister, T.R., 1970. The acritarchs and chitinozoa from the Wenlock and Ludlow Series of the Ludlow and Millichope areas, Shropshire. Pt. I. Palaeontol. Soc. Monogr., 124: 1--100. Loeblich, A.R., Jr. and Tappan, H., 1969. Acritarch excystment and surface ultrastructure with description of some Ordovician taxa. Rev. Esp. Micropaleontol., 1 : 45--57. Matsuoka, K., 1982. Dinoflagellate cysts in surface sediments of Omura Bay, West Kyushu, Japan. In: Fundamental Studies of the Effects on the Marine Environment of the Outbreaks of Red Tides. Reports of Environmental Sciences, B 148--R14-8, Mombusho, pp.197--204 (in Japanese, with English abstract). Morey-Gains, G. and Ruse, R.H., 1980. Encystment and reproduction of the predatory dinoflagellate, Polykrikos kofoidi Chatton (Gymnodiniales). Phycologia, 19: 230-232. Reid, P.C., 1978. Dinoflagellate cysts in the plankton. New Phytol., 80: 219--229. Reid, P.C. and Harland, R., 1977. Studies of Quaternary dinoflagellate cysts from the North Atlantic. In: W.C. Elsik (Editor), Contribution of Stratigraphic Palynology (with emphasis on North America), A.A.S.P. Contr. Ser. 5A., pp.147--165. Tappan, H., 1980. The Paleobiology of Plant Protists. W.H. Freeman and Company, San Francisco, CA, 1028 pp. Wall, D. and Dale, B., 1968. Modern dinoflagellate cysts and evolution of the peridiniales. Micropaleontology, 14: 265--304.