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Gonyaulacysta
From Fensome et al., 2019:
Gonyaulacysta, Deflandre, 1964, p.5030.
Emendations: Sarjeant, 1969, p.7–8; Stover and Evitt, 1978, p.157–158; Sarjeant, 1982b, p.27–28; Helenes and Lucas-Clark, 1997, p.175–176. Taxonomic senior synonym: Rhynchodiniopsis, by implication in Millioud (1969, p.428) who transferred the "type species" of Rhynchodiniopsis,
Rhynchodiniopsis aptiana, to Gonyaulacysta -- however, Lentin and Williams (1973, p.58,121) retained Gonyaulacysta.
Taxonomic junior synonyms: Nelchinopsis, according to Duxbury (1977, p.37) -- however, Stover and Williams (1987, p.11) retained Nelchinopsis; Psaligonyaulax, according to Below (1981a, p.52) -- however, Lentin and Williams (1981, p.235) retained Psaligonyaulax.
Although the "type species", Gonyaulacysta jurassica, was not validly transferred to Gonyaulacysta by Deflandre (1964), the generic name Gonyaulacysta was validly published by that author since it is based on a previously validly published species name.
Type: Deflandre, 1939a, pl.6, figs.2–3; text-figs.1–2, as Gonyaulax jurassica.
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Original description: [Deflandre, 1964]: (Translation: Stover and Evitt, 1978, p. 157):
Diagnosis:
I place in the genus Gonyaulacysta nov. gen. all the fossil species with Gonyaulax-like tabulation represented by thecae with projecting, more or less strongly ornamented crests (pectinate, spiny, denticulate, etc....) and provided with an archaeopyle (3rd pre-equatorial plate).
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Emended descriptions:
Sarjeant, 1966:
Diagnosis:
Proximate dinoflagellate cysts, spherical, ovoidal, ellipsoidal or polyhedral, with the tabulation 3-4`, 0-1a, 6``, 6c, 6```, 1p, 0-1 p.v., 1````. Cingulum strongly or weakly helicoid. Cingular plates (6c) well or poorly marked; ventral surface may show division into additional small plates. Sulcus generally but not constantly extending onto epitract. Apical horn frequently, but not constantly present; median and antapical horns lacking. Sutures in form of low ridges; bearing crests of varied form (smooth denticulate or spinous; perforate or imperforate); or marked by lines of spines of varied form. Height of spines or crests always less than 1/4 of shell width. A precingular archaeopyle formed by loss of plate 3``. (Archaeopyle not always present.) Surface smooth, granular, nodose, punctate or reticulate.
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Sarjeant, 1969:
Diagnosis:
Proximate dinoflagellate cysts, spherical, ovoidal, ellipsoidal or polyhedral, with an apical horn and the reflected tabulation 3-4`, 0-1a, 6``, 6c, 5-6```, 1p, 0-1p.v, 1````, 0-xs. Cingulum strongly or weakly helicoid; cingular plates well or poorly marked. Sulcus generally but not constantly extending on to the epitract; undivided or subdivided into a variable number of small plates.
Apical horn typically formed from the periphragm only, less frequently from both shell layers; rarely, an apical or antapical pericoel is present (but not both), but the two layers are most often otherwise in continuous contact. Median and antapical horns lacking. Sutures marked by low ridges; bearing crests of varied form (smooth, denticulate or spinous, perforate or imperforate); or marked by lines of spines of varied form. Height of spines or crests always less than 1/4 of shell width. A precingular single-plate archaeopyle, formed by loss of plate 3``, is developed, the operculum typically becoming wholly detached: in some individual specimens, the archaeopyle may not be developed. Surface of periphragm smooth, granular, nodose, punctate or reticulate; forms with a general spine cover are excluded.
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Stover and Evitt 1978:
Synopsis:
Cysts typically bicavate; endocyst subspherical to ellipsoidal; pericyst subpolygonal and generally elongate longitudinally, with a short to long apical horn. Paratabulation gonyaulacacean, indicated by parasutural septa with denticulate to spinulate crests; archeopyle precingular, Type P.
Description:
Shape: Elongate ellipsoidal to subpolygonal with a short to long apical horn; antapical end generally truncate.
Wall relationships: Cysts typically bicavate, although developed of epipericoel or hypopericoel may be lacking or reduced. In addition, tunnellike cavaties may extend toward paracingulum along parasutures.
Wall features: Parasutural septa with characteristic denticulate to spinulate crests; areas between septa smooth or punctoreticulate, or with scattered features of low relief; endophragm normally smooth.
Paratabulation: Indicated by parasutural features; gonyaulacacean, formula: 0-2pr, 3-4`, 0-1a, 6``, 6c, 5-6```, 1p, 1````, 0-1s; apical paraplates often difficult to distinguish.
Archeopyle: Precingular, Type P (3`` only); operculum free.
Paracingulum: Indicated by six subrectangular paraplates; ends of paracingulum typically strongly offset ventrally.
Parasulcus: Generally clearly delimited by parasutural septa, straight to S-shaped; posterior paraplate may be differentiated.
Size: Intermediate to large, generally the former.
Affinities:
Gonyaulacysta differs from Rhynchodiniopsis in being cavate and in lacking strongly developed spines at the intersections of parasutural features. Rhynchodiniopsis has an autophragm, and spinules in the gonal positions are longer (especially along the paracingulum) than those in intergonal locations.
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Sarjeant, 1982:
Diagnosis:
Proximate to proximochorate dinoflagellate cysts normally of small or intermediate, rarely of large, size. Ambitus subpolygonal to rounded subpolygonal or lozenge-shaped, consistently with an apical horn or prominence and with parasutural crests of variable form. Development of cavation at the apex universal, at the antapex variable to lacking; individual cysts may be apically cornucavate, epicavate, delphicavate or bicavate. Where a hypopericoel is developed, its length is always less than its breadth and the structure has no modifying effect on the ambitus of the hypotract, no angle being formed between the hypopericoel and the anterior portion of the hypotract.
Paratabulation 0-2pa, 3-4`, 0-1a, 6``, 6c-?7c, 6```, 1p, 0-1pv, 1````; the sulcus may also show some division into small paraplates.
Paraplate 4` is elongate and narrow, shorter than 1` and only having a small contact with 6``; the latter paraplate typically exhibits some measure of triangularity. The crest between 4` and 6`` intersects the right lateral crest of 1` in a position anterior, and usually markedly anterior, to the boundary of the latter paraplate with the sulcus. Cingulum strongly or weakly helicoid; between its two ends, the sulcus may be straight or in varying degree sigmoidal. Crests on parasutures raised, smooth, serrate or developed into denticles or spines of regular or irregular length and character; accessory crests feebly developed or (typically) lacking. Height of crests variable, but always less than 1/4 of the cyst width. Gonal spines of small to moderate height present or absent.
Surface of periphragm smooth, granular, nodose, punctate or reticulate; endophragm, where separate, typically smooth.
Archaeopyle single-plate precingular, formed by loss of paraplate 3``` (sic, but should be 3``); operculum reduced.
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Helenes and Lucas-Clark, 1997:
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Riding et al., 2022:
Emended diagnosis: Cavate, elongate, tabulate gonyaulacacean dinoflagellate cysts with an apical horn. The epicyst is markedly longer than the hypocyst, the cingulum being notably closer to the posterior pole than the anterior pole. The sulcus is L-type. Archaeopyle single-plate precingular, type P3′′. The operculum is free and formed from the endophragm only, because the periphragm representing the 3′′ plate is entirely absent. An opisthopyle which penetrates the ps plate may be present.
Emended description: Elongate, bilaterally symmetrical, usually dorsoventrally compressed dinoflagellate cysts with an ovoidal to subpolygonal (typically subpentagonal) pericyst, a prominent, truncate apical horn and amore or less straight to concave antapical margin. The endocyst is ovoidal,with orwithout a rounded apical protuberance. The epicyst is significantly longer than the hypocyst. Wall epicavate or bicavate but may occasionally be cornucavate or delphicavate respectively; locally suturocavate. Tabulation is indicated by sutural ridges or crests which may be discontinuous. Sutural features may be distally smooth, perforate or surmounted by denticles or small spines which, when developed, are distally pointed or bifurcate. The crests or ridges are typically markedly lower in height in the mid-ventral region. In the apical region the denticulation on the sutures, where developed, is reduced. The endophragm is moderately thick, with a smooth surface. The periphragm is markedly thinner than the endophragm and is normally smooth, but may bear isolated and scattered (nontabular) elements of low-relief such as granules and scabrae. Tabulation gonyaulacacean, formula 2pr, 4′, 1–2a, 6′′, 6c, 6′′′, 1p, 1′′′′, 5s; it differs from the standard gonyaulacalean pattern in the possession of one or two small anterior intercalary plates on the dorsal surface (Fensome et al., 1993; Fensome et al., 1996a, fig. 45). It exhibits neutral torsion and has a small porichnion at the 2pr/1′/4′ triple junction on the ventral side of the apical region. Archaeopyle precingular, type P3′′. The endoperculum may fall back into the empty endocyst. A perioperculum (the opercular piece representing the 3′′ plate in the periphragm) has never been observed, indicating that it was never developed (Eaton, 1984). Cingulum prominent and is located significantly closer to the antapex than to the apex; it is subdivided into six cingular plates and is laevorotatory, the displacement being typically equivalent to the width of the cingulum. The sulcus is mid-ventral and is L-type. It is normally straight (longitudinal), but occasionally may be slightly sigmoidal, delimited by low, sutural ridges; individual sulcal plates are not normally discernible. A circular to ellipsoid opisthopyle may be developed in the periphragm of the ps plate. The latter feature is normally only observable in species and specimens that exhibit a prominent hypopericoel, i.e. that are bicavate. Size: intermediate to large.
Comments: The genus Gonyaulacysta is herein placed in the subfamily Leptodinioideae due to its L-type ventral tabulation. Fensome et al. (1993, p. 91) assigned the genus to the subfamily Gonyaulacoideae, however this placement is inappropriate as it is confined to genera with S-type sulcuses. The five emendations of Gonyaulacysta cited previously successively provided more morphological detail than was given in the original description (Appendix 1 of the Supplementarymaterial). Sarjeant (1966, p. 140) incorrectly considered that Rhynchodiniopsis “...was, at the time of its publication, effectively a junior homonym of Gonyaulax, none of the characters cited warranting the creation of a new name” (clearly Sarjeant meant junior synonym). He proposed “that the name Rhynchodiniopsis be abandoned and the single species, R. aptiana ... be transferred to Gonyaulacysta.” However, as Stover and Evitt (1978, p. 275) pointed out, such a transfer would have been been nomenclaturally illegitimate as Rhynchodiniopsis aptiana is the type of Rhynchodiniopis, and that genus has priority over Gonyaulacysta; thus Stover and Evitt (1978, fig. 2) maintained the separation of Gonyaulacysta jurassica and Rhynchodiniopsis aptiana. We fully agree that Rhynchodiniopsis and Gonyaulacysta should be retained separately. Rhynchodiniopsis is an acavate to slightly cornucavate gonyaulacacean genus with an equatorial cingulum (e.g., Helenes, 1986, pl. 1, 1–6) and Gonyaulacysta is clearly not synonymous with it.
Stover and Evitt (1978, p. 275–278) also undertook a comprehensive and incisive investigation of the typematerial of Gonyaulacysta jurassica and Gonyaulacysta longicornis. They stated that theywere emending the genus, but did not provide a clear diagnosis or description labelled as such. William R. Evitt had visited Georges Deflandre in November 1959, and probably examined this material during his stay in Paris (Riding and Lucas-Clark, 2016, p. 37–39). The morphological analysis by Stover and Evitt (1978) was given as seven bullet points. Firstly, they described the bicavate and suturocavate cyst organisation and the shape of the endocyst. They noted that the midventral tabulation around the sulcus is consistently reduced, even partly suppressed. This phenomenon has also been observed in the closely related genus Tubotuberella (see Riding, 2012; Riding and Michoux, 2013). Williams (1964) and Stover and Evitt (1978) both noted the presence of one or two small anterior intercalary plates on the dorsal side of the epicyst. The narrowness of plate 4′ and the adjacent 6′′ was also mentioned. A prominent circular–ellipsoid opisthopyle is consistently present in the periphragmof the ps plate, and hence penetrates the antapical pericoel. This feature occupiesmost of the ps plate in both epicavate and bicavate cysts, but is only clearly visible in forms which are bicavate. Stover and Evitt (1978) commented that the detailed tabulation on the slender apical horn is difficult to precisely resolve. These authors also stated that the endoarchaeopyle is smaller than the periarchaeopyle. However, Eaton (1984, figs. 2–5) convincingly demonstrated that there is no perioperculum, and that the 3′′ plate is represented by a primary opening on the pericyst.
Helenes (1986) outlined 12 tabulation styles in gonyaulacacean dinoflagellates. One of these is the Jurassica pattern, which was named after Gonyaulacysta jurassica (Helenes, 1986, fig. 15). This pattern is based on characteristic plate configurations in the apical (pr/2′), ventral (1′/6′′) and antapical (symmetrical 1′′′′) regions (Helenes, 1986, fig. 15, table 1). This authormerged his Brixii, Ghermanii, Jurassica and Polyedra patterns into the Polyedra-Jurassica complex (Helenes, 1986, table 2). The most recent and comprehensive emendation of Gonyaulacysta was by Helenes and Lucas-Clark (1997, p. 175–176). These authors gave a synopsis and an emended description in six sections (i.e. shape, size, wall structure, archaeopyle, external features and tabulation), with most emphasis on the tabulation pattern. Gonyaulacysta has a distinctive tabulation with an L-type sulcus, contact between the 4′ and 6′′ plates, and the 1′ and 6′′ plates, a straight 1′′′ plate which lies within the sulcus and up to two anterior intercalary plates and a rectangular, symmetrical 1′′′′ plate (Helenes and Lucas-Clark, 1997, figs. 1–3; table 1). Fensome et al. (1993, p. 92) considered that Gonyaulacysta has S-type ventral organisation and so placed it in the subfamily Gonyaulacoideae. This is despite the fact that the line drawing of Gonyaulacysta jurassica in Fensome et al. (1993, fig. 94A) appears to have an L-type sulcus. Gonyaulacysta is distinguished from Stanfordella and Wrevittia by key plate configurations, cavation style, equatorial cross section and the shape of the sulcus (Helenes and Lucas-Clark, 1997, table 1). The two ventral plate configurations proposed by Evitt (1985) are discussed in Section 4 below. In our view, the most characteristic feature of Gonyaulacysta is the unequal lengths of the epicyst and hypocyst, the former being much longer. The overwhelming majority of gonyaulacacean and peridiniacean fossil dinoflagellates have subequal epicysts and hypocysts, or the epicyst is shorter than the hypocyst (e.g., Lentin and Williams, 1976; Bujak and Davies, 1983; Jan du Chêne et al., 1986). In Gonyaulacysta, the epicyst approaches twice the length of the hypocyst (Figs. 1, 2). This highly unusual phenomenon has previously beenmentioned by Riding and Helby (2001a, p. 151), Riding (2005a, p. 14) and Riding and Lucas-Clark (2016, p. 79). In terms of tabulation, the apical region exhibits two preapical plates, two anterior intercalary plates and a porichnion (Fig. 1; Stover and Evitt, 1978, fig. 2; Evitt, 1985, figs. 5.16D, 10.9B; Helenes, 1986, fig. 15; Fensome et al., 1993, figs. 84B, 94; Helenes and Lucas-Clark, 1997, fig. 3). All these small areas are frequently difficult to observe in many specimens using transmitted light microscopy. Specifically, the porichnion at the 2pr/1′/4′ triple junction on the ventral side of the apical region is normally only visible in wellpreserved material using a scanning electron microscope (Helenes, 1986, pl. 4, 2). This small pore is a reflection of the adelopore of motile dinoflagellates and was first described by Evitt (1985, p. 74). The original, and all the five emended diagnoses and descriptions of Gonyaulacysta, are given in full in Appendix 1 of the the Supplementary material. We deem it necessary to emend Gonyaulacysta herein in order to stress the variety of cavation, the epicyst that ismuch longer than the hypocyst, the lack of a perioperculum and the possible presence of an opisthopyle in the ps plate. The genus Gonyaulacysta is cosmopolitan, and has a highly characteristic morphology; the eight species outlined herein form a tightly defined genus which is confined to the Middle and Late Jurassic. The oldest species, Gonyaulacysta adecta, is largely of Middle Jurassic age, but the other species are confined to the Late Jurassic. The genus is most abundant in theOxfordian (Fig. 3). The species are principally differentiated on the morphology of the sutural ridges/crests and the cavation style. Due to the specificmorphology and tabulation of Gonyaulacysta recognised herein, the transfer of 18 species into genera more appropriate to their morphology is considered to be neccessary. Additionally, three previous transfers of species into Gonyaulacysta are not supported herein.
Comparison: Gonyaulacysta is easily distinguished from acavate gonyaulacaean genera with single-plate precingular archaeopyles, such as Acanthaulax, Apteodinium, Leptodinium, Rhynchodiniopsis and Trichodinium, by exhibiting clear separation of the endophragm and periphragm. However, Gonyaulacysta shares some features with other cavate gonyaulacacean genera. For example, Psaligonyaulax and Tubotuberella are also prominently bicavate and often exhibit sutural crests and ridges. But, like most other dinoflagellate genera, the cingulums of Psaligonyaulax and Tubotuberella are positioned equatorially, such that the epicyst and hypocyst are of more or less equal length. Psaligonyaulax lacks an opisthopyle, and the hypocystal opening in the periphragm of Tubotuberella is in the 1′′′′ plate (Jan du Chene et al., 1986, pl. 123). Stanfordella and Wrevittia are also superficially similar to Gonyaulacysta, but have circular cross sections, equatorial cingulums and S-type ventral tabulation. Despite the latter feature, these genera were place in the subfamily Leptodinioideae which is characterised by L-type sulcuses by Helenes and Lucas-Clark (1997). They also differ in having a cornucavate epicyst and several species have suturocavate hypocysts. Moreover, they typically lack any anterior intercalary plates and differ in several key plate contacts (Helenes and Lucas-Clark, 1997, figs. 1, 2; table 1). Duxbury (1977, p. 37) deemed the monotypic genus Nelchinopsis to be a taxonomic junior synonym of Gonyaulacysta. Nelchinopsis, which was retained as a separate genus by Stover and Williams (1987, p. 11), is holocavate and its archaeopyle type is not known with certainty (Harding, 1996, p. 353). Triblastula displays a small, subspherical endocyst, is strongly bicavate with extensive pericoels and has prominent processes surrounding the cingulum. Hystrichosphaeropsis is strongly bicavate and can be circumcavate with extremely large pericoels; it also has a subspherical endocyst, lacks sutural ornamentation, and has typically weakly expressed tabulation.
Gonyaulacysta, Deflandre, 1964, p.5030.
Emendations: Sarjeant, 1969, p.7–8; Stover and Evitt, 1978, p.157–158; Sarjeant, 1982b, p.27–28; Helenes and Lucas-Clark, 1997, p.175–176. Taxonomic senior synonym: Rhynchodiniopsis, by implication in Millioud (1969, p.428) who transferred the "type species" of Rhynchodiniopsis,
Rhynchodiniopsis aptiana, to Gonyaulacysta -- however, Lentin and Williams (1973, p.58,121) retained Gonyaulacysta.
Taxonomic junior synonyms: Nelchinopsis, according to Duxbury (1977, p.37) -- however, Stover and Williams (1987, p.11) retained Nelchinopsis; Psaligonyaulax, according to Below (1981a, p.52) -- however, Lentin and Williams (1981, p.235) retained Psaligonyaulax.
Although the "type species", Gonyaulacysta jurassica, was not validly transferred to Gonyaulacysta by Deflandre (1964), the generic name Gonyaulacysta was validly published by that author since it is based on a previously validly published species name.
Type: Deflandre, 1939a, pl.6, figs.2–3; text-figs.1–2, as Gonyaulax jurassica.
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Original description: [Deflandre, 1964]: (Translation: Stover and Evitt, 1978, p. 157):
Diagnosis:
I place in the genus Gonyaulacysta nov. gen. all the fossil species with Gonyaulax-like tabulation represented by thecae with projecting, more or less strongly ornamented crests (pectinate, spiny, denticulate, etc....) and provided with an archaeopyle (3rd pre-equatorial plate).
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Emended descriptions:
Sarjeant, 1966:
Diagnosis:
Proximate dinoflagellate cysts, spherical, ovoidal, ellipsoidal or polyhedral, with the tabulation 3-4`, 0-1a, 6``, 6c, 6```, 1p, 0-1 p.v., 1````. Cingulum strongly or weakly helicoid. Cingular plates (6c) well or poorly marked; ventral surface may show division into additional small plates. Sulcus generally but not constantly extending onto epitract. Apical horn frequently, but not constantly present; median and antapical horns lacking. Sutures in form of low ridges; bearing crests of varied form (smooth denticulate or spinous; perforate or imperforate); or marked by lines of spines of varied form. Height of spines or crests always less than 1/4 of shell width. A precingular archaeopyle formed by loss of plate 3``. (Archaeopyle not always present.) Surface smooth, granular, nodose, punctate or reticulate.
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Sarjeant, 1969:
Diagnosis:
Proximate dinoflagellate cysts, spherical, ovoidal, ellipsoidal or polyhedral, with an apical horn and the reflected tabulation 3-4`, 0-1a, 6``, 6c, 5-6```, 1p, 0-1p.v, 1````, 0-xs. Cingulum strongly or weakly helicoid; cingular plates well or poorly marked. Sulcus generally but not constantly extending on to the epitract; undivided or subdivided into a variable number of small plates.
Apical horn typically formed from the periphragm only, less frequently from both shell layers; rarely, an apical or antapical pericoel is present (but not both), but the two layers are most often otherwise in continuous contact. Median and antapical horns lacking. Sutures marked by low ridges; bearing crests of varied form (smooth, denticulate or spinous, perforate or imperforate); or marked by lines of spines of varied form. Height of spines or crests always less than 1/4 of shell width. A precingular single-plate archaeopyle, formed by loss of plate 3``, is developed, the operculum typically becoming wholly detached: in some individual specimens, the archaeopyle may not be developed. Surface of periphragm smooth, granular, nodose, punctate or reticulate; forms with a general spine cover are excluded.
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Stover and Evitt 1978:
Synopsis:
Cysts typically bicavate; endocyst subspherical to ellipsoidal; pericyst subpolygonal and generally elongate longitudinally, with a short to long apical horn. Paratabulation gonyaulacacean, indicated by parasutural septa with denticulate to spinulate crests; archeopyle precingular, Type P.
Description:
Shape: Elongate ellipsoidal to subpolygonal with a short to long apical horn; antapical end generally truncate.
Wall relationships: Cysts typically bicavate, although developed of epipericoel or hypopericoel may be lacking or reduced. In addition, tunnellike cavaties may extend toward paracingulum along parasutures.
Wall features: Parasutural septa with characteristic denticulate to spinulate crests; areas between septa smooth or punctoreticulate, or with scattered features of low relief; endophragm normally smooth.
Paratabulation: Indicated by parasutural features; gonyaulacacean, formula: 0-2pr, 3-4`, 0-1a, 6``, 6c, 5-6```, 1p, 1````, 0-1s; apical paraplates often difficult to distinguish.
Archeopyle: Precingular, Type P (3`` only); operculum free.
Paracingulum: Indicated by six subrectangular paraplates; ends of paracingulum typically strongly offset ventrally.
Parasulcus: Generally clearly delimited by parasutural septa, straight to S-shaped; posterior paraplate may be differentiated.
Size: Intermediate to large, generally the former.
Affinities:
Gonyaulacysta differs from Rhynchodiniopsis in being cavate and in lacking strongly developed spines at the intersections of parasutural features. Rhynchodiniopsis has an autophragm, and spinules in the gonal positions are longer (especially along the paracingulum) than those in intergonal locations.
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Sarjeant, 1982:
Diagnosis:
Proximate to proximochorate dinoflagellate cysts normally of small or intermediate, rarely of large, size. Ambitus subpolygonal to rounded subpolygonal or lozenge-shaped, consistently with an apical horn or prominence and with parasutural crests of variable form. Development of cavation at the apex universal, at the antapex variable to lacking; individual cysts may be apically cornucavate, epicavate, delphicavate or bicavate. Where a hypopericoel is developed, its length is always less than its breadth and the structure has no modifying effect on the ambitus of the hypotract, no angle being formed between the hypopericoel and the anterior portion of the hypotract.
Paratabulation 0-2pa, 3-4`, 0-1a, 6``, 6c-?7c, 6```, 1p, 0-1pv, 1````; the sulcus may also show some division into small paraplates.
Paraplate 4` is elongate and narrow, shorter than 1` and only having a small contact with 6``; the latter paraplate typically exhibits some measure of triangularity. The crest between 4` and 6`` intersects the right lateral crest of 1` in a position anterior, and usually markedly anterior, to the boundary of the latter paraplate with the sulcus. Cingulum strongly or weakly helicoid; between its two ends, the sulcus may be straight or in varying degree sigmoidal. Crests on parasutures raised, smooth, serrate or developed into denticles or spines of regular or irregular length and character; accessory crests feebly developed or (typically) lacking. Height of crests variable, but always less than 1/4 of the cyst width. Gonal spines of small to moderate height present or absent.
Surface of periphragm smooth, granular, nodose, punctate or reticulate; endophragm, where separate, typically smooth.
Archaeopyle single-plate precingular, formed by loss of paraplate 3``` (sic, but should be 3``); operculum reduced.
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Helenes and Lucas-Clark, 1997:
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Riding et al., 2022:
Emended diagnosis: Cavate, elongate, tabulate gonyaulacacean dinoflagellate cysts with an apical horn. The epicyst is markedly longer than the hypocyst, the cingulum being notably closer to the posterior pole than the anterior pole. The sulcus is L-type. Archaeopyle single-plate precingular, type P3′′. The operculum is free and formed from the endophragm only, because the periphragm representing the 3′′ plate is entirely absent. An opisthopyle which penetrates the ps plate may be present.
Emended description: Elongate, bilaterally symmetrical, usually dorsoventrally compressed dinoflagellate cysts with an ovoidal to subpolygonal (typically subpentagonal) pericyst, a prominent, truncate apical horn and amore or less straight to concave antapical margin. The endocyst is ovoidal,with orwithout a rounded apical protuberance. The epicyst is significantly longer than the hypocyst. Wall epicavate or bicavate but may occasionally be cornucavate or delphicavate respectively; locally suturocavate. Tabulation is indicated by sutural ridges or crests which may be discontinuous. Sutural features may be distally smooth, perforate or surmounted by denticles or small spines which, when developed, are distally pointed or bifurcate. The crests or ridges are typically markedly lower in height in the mid-ventral region. In the apical region the denticulation on the sutures, where developed, is reduced. The endophragm is moderately thick, with a smooth surface. The periphragm is markedly thinner than the endophragm and is normally smooth, but may bear isolated and scattered (nontabular) elements of low-relief such as granules and scabrae. Tabulation gonyaulacacean, formula 2pr, 4′, 1–2a, 6′′, 6c, 6′′′, 1p, 1′′′′, 5s; it differs from the standard gonyaulacalean pattern in the possession of one or two small anterior intercalary plates on the dorsal surface (Fensome et al., 1993; Fensome et al., 1996a, fig. 45). It exhibits neutral torsion and has a small porichnion at the 2pr/1′/4′ triple junction on the ventral side of the apical region. Archaeopyle precingular, type P3′′. The endoperculum may fall back into the empty endocyst. A perioperculum (the opercular piece representing the 3′′ plate in the periphragm) has never been observed, indicating that it was never developed (Eaton, 1984). Cingulum prominent and is located significantly closer to the antapex than to the apex; it is subdivided into six cingular plates and is laevorotatory, the displacement being typically equivalent to the width of the cingulum. The sulcus is mid-ventral and is L-type. It is normally straight (longitudinal), but occasionally may be slightly sigmoidal, delimited by low, sutural ridges; individual sulcal plates are not normally discernible. A circular to ellipsoid opisthopyle may be developed in the periphragm of the ps plate. The latter feature is normally only observable in species and specimens that exhibit a prominent hypopericoel, i.e. that are bicavate. Size: intermediate to large.
Comments: The genus Gonyaulacysta is herein placed in the subfamily Leptodinioideae due to its L-type ventral tabulation. Fensome et al. (1993, p. 91) assigned the genus to the subfamily Gonyaulacoideae, however this placement is inappropriate as it is confined to genera with S-type sulcuses. The five emendations of Gonyaulacysta cited previously successively provided more morphological detail than was given in the original description (Appendix 1 of the Supplementarymaterial). Sarjeant (1966, p. 140) incorrectly considered that Rhynchodiniopsis “...was, at the time of its publication, effectively a junior homonym of Gonyaulax, none of the characters cited warranting the creation of a new name” (clearly Sarjeant meant junior synonym). He proposed “that the name Rhynchodiniopsis be abandoned and the single species, R. aptiana ... be transferred to Gonyaulacysta.” However, as Stover and Evitt (1978, p. 275) pointed out, such a transfer would have been been nomenclaturally illegitimate as Rhynchodiniopsis aptiana is the type of Rhynchodiniopis, and that genus has priority over Gonyaulacysta; thus Stover and Evitt (1978, fig. 2) maintained the separation of Gonyaulacysta jurassica and Rhynchodiniopsis aptiana. We fully agree that Rhynchodiniopsis and Gonyaulacysta should be retained separately. Rhynchodiniopsis is an acavate to slightly cornucavate gonyaulacacean genus with an equatorial cingulum (e.g., Helenes, 1986, pl. 1, 1–6) and Gonyaulacysta is clearly not synonymous with it.
Stover and Evitt (1978, p. 275–278) also undertook a comprehensive and incisive investigation of the typematerial of Gonyaulacysta jurassica and Gonyaulacysta longicornis. They stated that theywere emending the genus, but did not provide a clear diagnosis or description labelled as such. William R. Evitt had visited Georges Deflandre in November 1959, and probably examined this material during his stay in Paris (Riding and Lucas-Clark, 2016, p. 37–39). The morphological analysis by Stover and Evitt (1978) was given as seven bullet points. Firstly, they described the bicavate and suturocavate cyst organisation and the shape of the endocyst. They noted that the midventral tabulation around the sulcus is consistently reduced, even partly suppressed. This phenomenon has also been observed in the closely related genus Tubotuberella (see Riding, 2012; Riding and Michoux, 2013). Williams (1964) and Stover and Evitt (1978) both noted the presence of one or two small anterior intercalary plates on the dorsal side of the epicyst. The narrowness of plate 4′ and the adjacent 6′′ was also mentioned. A prominent circular–ellipsoid opisthopyle is consistently present in the periphragmof the ps plate, and hence penetrates the antapical pericoel. This feature occupiesmost of the ps plate in both epicavate and bicavate cysts, but is only clearly visible in forms which are bicavate. Stover and Evitt (1978) commented that the detailed tabulation on the slender apical horn is difficult to precisely resolve. These authors also stated that the endoarchaeopyle is smaller than the periarchaeopyle. However, Eaton (1984, figs. 2–5) convincingly demonstrated that there is no perioperculum, and that the 3′′ plate is represented by a primary opening on the pericyst.
Helenes (1986) outlined 12 tabulation styles in gonyaulacacean dinoflagellates. One of these is the Jurassica pattern, which was named after Gonyaulacysta jurassica (Helenes, 1986, fig. 15). This pattern is based on characteristic plate configurations in the apical (pr/2′), ventral (1′/6′′) and antapical (symmetrical 1′′′′) regions (Helenes, 1986, fig. 15, table 1). This authormerged his Brixii, Ghermanii, Jurassica and Polyedra patterns into the Polyedra-Jurassica complex (Helenes, 1986, table 2). The most recent and comprehensive emendation of Gonyaulacysta was by Helenes and Lucas-Clark (1997, p. 175–176). These authors gave a synopsis and an emended description in six sections (i.e. shape, size, wall structure, archaeopyle, external features and tabulation), with most emphasis on the tabulation pattern. Gonyaulacysta has a distinctive tabulation with an L-type sulcus, contact between the 4′ and 6′′ plates, and the 1′ and 6′′ plates, a straight 1′′′ plate which lies within the sulcus and up to two anterior intercalary plates and a rectangular, symmetrical 1′′′′ plate (Helenes and Lucas-Clark, 1997, figs. 1–3; table 1). Fensome et al. (1993, p. 92) considered that Gonyaulacysta has S-type ventral organisation and so placed it in the subfamily Gonyaulacoideae. This is despite the fact that the line drawing of Gonyaulacysta jurassica in Fensome et al. (1993, fig. 94A) appears to have an L-type sulcus. Gonyaulacysta is distinguished from Stanfordella and Wrevittia by key plate configurations, cavation style, equatorial cross section and the shape of the sulcus (Helenes and Lucas-Clark, 1997, table 1). The two ventral plate configurations proposed by Evitt (1985) are discussed in Section 4 below. In our view, the most characteristic feature of Gonyaulacysta is the unequal lengths of the epicyst and hypocyst, the former being much longer. The overwhelming majority of gonyaulacacean and peridiniacean fossil dinoflagellates have subequal epicysts and hypocysts, or the epicyst is shorter than the hypocyst (e.g., Lentin and Williams, 1976; Bujak and Davies, 1983; Jan du Chêne et al., 1986). In Gonyaulacysta, the epicyst approaches twice the length of the hypocyst (Figs. 1, 2). This highly unusual phenomenon has previously beenmentioned by Riding and Helby (2001a, p. 151), Riding (2005a, p. 14) and Riding and Lucas-Clark (2016, p. 79). In terms of tabulation, the apical region exhibits two preapical plates, two anterior intercalary plates and a porichnion (Fig. 1; Stover and Evitt, 1978, fig. 2; Evitt, 1985, figs. 5.16D, 10.9B; Helenes, 1986, fig. 15; Fensome et al., 1993, figs. 84B, 94; Helenes and Lucas-Clark, 1997, fig. 3). All these small areas are frequently difficult to observe in many specimens using transmitted light microscopy. Specifically, the porichnion at the 2pr/1′/4′ triple junction on the ventral side of the apical region is normally only visible in wellpreserved material using a scanning electron microscope (Helenes, 1986, pl. 4, 2). This small pore is a reflection of the adelopore of motile dinoflagellates and was first described by Evitt (1985, p. 74). The original, and all the five emended diagnoses and descriptions of Gonyaulacysta, are given in full in Appendix 1 of the the Supplementary material. We deem it necessary to emend Gonyaulacysta herein in order to stress the variety of cavation, the epicyst that ismuch longer than the hypocyst, the lack of a perioperculum and the possible presence of an opisthopyle in the ps plate. The genus Gonyaulacysta is cosmopolitan, and has a highly characteristic morphology; the eight species outlined herein form a tightly defined genus which is confined to the Middle and Late Jurassic. The oldest species, Gonyaulacysta adecta, is largely of Middle Jurassic age, but the other species are confined to the Late Jurassic. The genus is most abundant in theOxfordian (Fig. 3). The species are principally differentiated on the morphology of the sutural ridges/crests and the cavation style. Due to the specificmorphology and tabulation of Gonyaulacysta recognised herein, the transfer of 18 species into genera more appropriate to their morphology is considered to be neccessary. Additionally, three previous transfers of species into Gonyaulacysta are not supported herein.
Comparison: Gonyaulacysta is easily distinguished from acavate gonyaulacaean genera with single-plate precingular archaeopyles, such as Acanthaulax, Apteodinium, Leptodinium, Rhynchodiniopsis and Trichodinium, by exhibiting clear separation of the endophragm and periphragm. However, Gonyaulacysta shares some features with other cavate gonyaulacacean genera. For example, Psaligonyaulax and Tubotuberella are also prominently bicavate and often exhibit sutural crests and ridges. But, like most other dinoflagellate genera, the cingulums of Psaligonyaulax and Tubotuberella are positioned equatorially, such that the epicyst and hypocyst are of more or less equal length. Psaligonyaulax lacks an opisthopyle, and the hypocystal opening in the periphragm of Tubotuberella is in the 1′′′′ plate (Jan du Chene et al., 1986, pl. 123). Stanfordella and Wrevittia are also superficially similar to Gonyaulacysta, but have circular cross sections, equatorial cingulums and S-type ventral tabulation. Despite the latter feature, these genera were place in the subfamily Leptodinioideae which is characterised by L-type sulcuses by Helenes and Lucas-Clark (1997). They also differ in having a cornucavate epicyst and several species have suturocavate hypocysts. Moreover, they typically lack any anterior intercalary plates and differ in several key plate contacts (Helenes and Lucas-Clark, 1997, figs. 1, 2; table 1). Duxbury (1977, p. 37) deemed the monotypic genus Nelchinopsis to be a taxonomic junior synonym of Gonyaulacysta. Nelchinopsis, which was retained as a separate genus by Stover and Williams (1987, p. 11), is holocavate and its archaeopyle type is not known with certainty (Harding, 1996, p. 353). Triblastula displays a small, subspherical endocyst, is strongly bicavate with extensive pericoels and has prominent processes surrounding the cingulum. Hystrichosphaeropsis is strongly bicavate and can be circumcavate with extremely large pericoels; it also has a subspherical endocyst, lacks sutural ornamentation, and has typically weakly expressed tabulation.