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Gonyaulacysta obscura
From Fensome et al., 2019:
Gonyaulacysta? obscura (Lejeune-Carpentier, 1946, p.B191, figs.3–5) Sarjeant, 1969, p.10. Emendation: Lejeune-Carpentier and Sarjeant, 1981, p.4, as Gonyaulacysta obscura. Holotype: Lejeune-Carpentier, 1946, figs.3–4; Lejeune-Carpentier and Sarjeant, 1981, pl.2, figs.3–4; text-fig.2. Originally Gonyaulax (Appendix B), subsequently Gonyaulacysta, thirdly (and now) Gonyaulacysta?, fourthly Millioudodinium. Questionable assignment: Stover and Evitt (1978, p.158). This combination was not validly published in Sarjeant (1966b, p.131), since that author did not fully reference the basionym. Age: Senonian.
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Original description (Lejeune-Carpentier, 1946) (translated from French):
Gonyaulax obscura n. sp. (fig. 8 to 5) = Palaeoperidium ventriosum Defl. 1937 nec. O. We. 1933.
Theca with a polygonal outline, showing a slight dorsiventral flattening. The epitheca is more developed and more angular than the hypotheca, surmounted by a broad-based apical horn.
A strongly helical transverse groove, its ends offset by nearly twice its width. This groove is shallow and bordered by thick, slightly raised lips.
A narrow and deep ventral area, clearly curved into a "knee," extends far into the hypotheca and descends into the epitheca to a height approximately equal to the width of a belt.
The tabulation is extremely difficult to decipher due to the opacity conferred on the shell by its thickness and sculpture. Here, subject to future corrections, is the formula we believe we can use: 3' and 1a (or 4'?), 6", 6"', 1p, 1"". Plate 1' is very elongated; to its right, another equally narrow plate, which we were unable to limit on the apical side, appears to be an intercalary. The last of the precingulates, 6", is very small. Plate 5" is also not very developed (). As with most Jurassic Gonyaulax studied by Deflandre (1938), plate 3" is missing from our specimens; however, one specimen was intact and was chosen as the type of the species. 1'" is particularly narrow and arranged obliquely relative to the longitudinal axis. The intercalary, 1p, extends under the first two postcingulates. There appears to be only one antapical. Remarkable is the considerable thickness of the membrane, a feature already clearly demonstrated in a figure by Deflandre (1936, pl. V, fig. 4). This thickness, according to the French author, could be due to "partial hydrolysis before fossilization." If this is truly an alteration, it is surprising that it has uniformly affected all the specimens from various sources examined so far. This particular condition of the shell is in fact quite similar to that which also distinguishes Sopngodinium delitiense (Ehr.). Observed from the front, the theca shows a coarse reticulation, forming ribs in places that blend in all the more easily with the sutures, since the relief of the latter is not very pronounced. Were it not for their relative transparency, the sutures could not really be distinguished from the other details of the shell. Dimensions:
Length, including horn = 52 to 53 μ (a single specimen reaches 62 μ);
Width in central view, including the edges of the girdle = 39 to 47 μ;
Width in profile = approximately 35 μ.
Material.
Seven specimens from flints collected from the Mortiau quarry in Cuesmes, Spiennes stratum (personal collection, flints CXII and CXIII).
Despite extensive research in the flints of the Limburg Basin, we have never managed to discover a single specimen of G. obscura there. It seems that O. Wetzel also never encountered it in Baltic flints. Could this indicate a localization of the species in the flints of Western Europe? Or a stricter stratigraphic distribution than has been considered so far?
Affinities. We do not believe it is necessary to dwell on the differences separating the species we have just defined from P. ventriosum O. We. We have seen that these two Peridinians could even belong to different genera. Eodinia pachytheca, a Jurassic species published in 1936 by A. Eisenack, resembles our G. obscura quite closely. The general outline, thickness, and sculpture of the theca, according to the photographs (fig. 1-3, p. 73) reproduced from it, must be of the same type. The tabulation is very indistinct; the author even believed it to be nonexistent, as is the case with certain primitive forms of Dinoflagellates. The apical horn is shorter. The transverse groove is very weakly marked. The size is much larger than that of our species, more than double.
Gonyaulacysta? obscura (Lejeune-Carpentier, 1946, p.B191, figs.3–5) Sarjeant, 1969, p.10. Emendation: Lejeune-Carpentier and Sarjeant, 1981, p.4, as Gonyaulacysta obscura. Holotype: Lejeune-Carpentier, 1946, figs.3–4; Lejeune-Carpentier and Sarjeant, 1981, pl.2, figs.3–4; text-fig.2. Originally Gonyaulax (Appendix B), subsequently Gonyaulacysta, thirdly (and now) Gonyaulacysta?, fourthly Millioudodinium. Questionable assignment: Stover and Evitt (1978, p.158). This combination was not validly published in Sarjeant (1966b, p.131), since that author did not fully reference the basionym. Age: Senonian.
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Original description (Lejeune-Carpentier, 1946) (translated from French):
Gonyaulax obscura n. sp. (fig. 8 to 5) = Palaeoperidium ventriosum Defl. 1937 nec. O. We. 1933.
Theca with a polygonal outline, showing a slight dorsiventral flattening. The epitheca is more developed and more angular than the hypotheca, surmounted by a broad-based apical horn.
A strongly helical transverse groove, its ends offset by nearly twice its width. This groove is shallow and bordered by thick, slightly raised lips.
A narrow and deep ventral area, clearly curved into a "knee," extends far into the hypotheca and descends into the epitheca to a height approximately equal to the width of a belt.
The tabulation is extremely difficult to decipher due to the opacity conferred on the shell by its thickness and sculpture. Here, subject to future corrections, is the formula we believe we can use: 3' and 1a (or 4'?), 6", 6"', 1p, 1"". Plate 1' is very elongated; to its right, another equally narrow plate, which we were unable to limit on the apical side, appears to be an intercalary. The last of the precingulates, 6", is very small. Plate 5" is also not very developed (). As with most Jurassic Gonyaulax studied by Deflandre (1938), plate 3" is missing from our specimens; however, one specimen was intact and was chosen as the type of the species. 1'" is particularly narrow and arranged obliquely relative to the longitudinal axis. The intercalary, 1p, extends under the first two postcingulates. There appears to be only one antapical. Remarkable is the considerable thickness of the membrane, a feature already clearly demonstrated in a figure by Deflandre (1936, pl. V, fig. 4). This thickness, according to the French author, could be due to "partial hydrolysis before fossilization." If this is truly an alteration, it is surprising that it has uniformly affected all the specimens from various sources examined so far. This particular condition of the shell is in fact quite similar to that which also distinguishes Sopngodinium delitiense (Ehr.). Observed from the front, the theca shows a coarse reticulation, forming ribs in places that blend in all the more easily with the sutures, since the relief of the latter is not very pronounced. Were it not for their relative transparency, the sutures could not really be distinguished from the other details of the shell. Dimensions:
Length, including horn = 52 to 53 μ (a single specimen reaches 62 μ);
Width in central view, including the edges of the girdle = 39 to 47 μ;
Width in profile = approximately 35 μ.
Material.
Seven specimens from flints collected from the Mortiau quarry in Cuesmes, Spiennes stratum (personal collection, flints CXII and CXIII).
Despite extensive research in the flints of the Limburg Basin, we have never managed to discover a single specimen of G. obscura there. It seems that O. Wetzel also never encountered it in Baltic flints. Could this indicate a localization of the species in the flints of Western Europe? Or a stricter stratigraphic distribution than has been considered so far?
Affinities. We do not believe it is necessary to dwell on the differences separating the species we have just defined from P. ventriosum O. We. We have seen that these two Peridinians could even belong to different genera. Eodinia pachytheca, a Jurassic species published in 1936 by A. Eisenack, resembles our G. obscura quite closely. The general outline, thickness, and sculpture of the theca, according to the photographs (fig. 1-3, p. 73) reproduced from it, must be of the same type. The tabulation is very indistinct; the author even believed it to be nonexistent, as is the case with certain primitive forms of Dinoflagellates. The apical horn is shorter. The transverse groove is very weakly marked. The size is much larger than that of our species, more than double.