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Dinogymnium heterocostatum ssp. heterocostatum
Dinogymnium heterocostatum ssp. heterocostatum
Autonym.
Originally Gymnodinium (Appendix B), subsequently (and now) Dinogymnium.
Holotype: Deflandre, 1935, text-fig.6; Deflandre, 1936b, pl.2, fig.6.
Age: ?Senonian.
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Original description: [Deflandre, 1936b] (translated from French):
GYMNODINIUM HETEROCOSTATUM Deflandre.
Plate II, fig. 6.
G. DEFLANDRE, Bulletin Biologique, LXIX, 1935, pp. 225, 226, fig. 6. - Les flagellates fossiles, 1936, p. 56, fig. 93.
Holotype: AF 58, Silex S. 35, pebble, Paris.
Paratype: AH 73, Senonian flint, Beynes chalk. (S.-et-O.).
The best-preserved specimen is presented in lateral view in the flake that contains it, and the longitudinal groove is located on the right (Plate II, fig. 6). As in the previous species, the epitheca and hypotheca are approximately the same size. In lateral view, as seen in the figure, the epitheca is bell-shaped and symmetrical, while the hypotheca, clearly asymmetrical, is shaped like a large cone, whose right side, adjacent to the longitudinal groove, is roughly straight. The transverse groove is narrow, but very deep. As far as can be judged by the focus, this groove is very slightly helical, and the longitudinal groove appears to develop at length on both the epitheca and the hypotheca, approaching quite close to the poles. The frontal view, which cannot be seen, but of which we can gain some knowledge by breaking it down into successive optical planes or sections using the micrometer screw, appears to be able to be described as follows: the epitheca would be conical, with a wide base and very concave sides, converging at a point towards the apex which would form a sort of carina. On the contrary, the hypotheca, bulging, would have convex sides, orienting fairly regularly towards a broadly rounded antapical pole. A subsequent examination of a specimen in oblique apical view fully confirmed this description of the epitheca. The membrane is adorned with a system of robust striations or ribs, of varying strength and length. The longest end towards the poles, and shorter ones alternate between them. In the specimen described, the long ribs of the epitheca reach the apex, while on the hypotheca, approximately one in two stops around the halfway or second third of the way down this hypotheca.
Three specimens were found in a flint pebble (? Senonian) collected in Paris. A fourth, which appears to belong to the same species, comes from a Senonian flint from the Beynes chalk (SW). In three measurable specimens, the length varies between approximately 60 and 65 μm.
The uncertainty, which cannot be completely resolved with regard to the frontal view, hardly allows for comparison with extant species. However, one can cite, as a relative, Gymnodinium diploconus Schütt (Schiller, 1932, op. cit., p. 353, fig. 359 a-c), which measures 57 to 80 μm, and whose representations, moreover, are not very concordant, present some of the characteristics of Gymnodinium heterocostatum.
But, here again, the strong striations of the membrane of the latter reject any attempt at identification between the two species.
Autonym.
Originally Gymnodinium (Appendix B), subsequently (and now) Dinogymnium.
Holotype: Deflandre, 1935, text-fig.6; Deflandre, 1936b, pl.2, fig.6.
Age: ?Senonian.
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Original description: [Deflandre, 1936b] (translated from French):
GYMNODINIUM HETEROCOSTATUM Deflandre.
Plate II, fig. 6.
G. DEFLANDRE, Bulletin Biologique, LXIX, 1935, pp. 225, 226, fig. 6. - Les flagellates fossiles, 1936, p. 56, fig. 93.
Holotype: AF 58, Silex S. 35, pebble, Paris.
Paratype: AH 73, Senonian flint, Beynes chalk. (S.-et-O.).
The best-preserved specimen is presented in lateral view in the flake that contains it, and the longitudinal groove is located on the right (Plate II, fig. 6). As in the previous species, the epitheca and hypotheca are approximately the same size. In lateral view, as seen in the figure, the epitheca is bell-shaped and symmetrical, while the hypotheca, clearly asymmetrical, is shaped like a large cone, whose right side, adjacent to the longitudinal groove, is roughly straight. The transverse groove is narrow, but very deep. As far as can be judged by the focus, this groove is very slightly helical, and the longitudinal groove appears to develop at length on both the epitheca and the hypotheca, approaching quite close to the poles. The frontal view, which cannot be seen, but of which we can gain some knowledge by breaking it down into successive optical planes or sections using the micrometer screw, appears to be able to be described as follows: the epitheca would be conical, with a wide base and very concave sides, converging at a point towards the apex which would form a sort of carina. On the contrary, the hypotheca, bulging, would have convex sides, orienting fairly regularly towards a broadly rounded antapical pole. A subsequent examination of a specimen in oblique apical view fully confirmed this description of the epitheca. The membrane is adorned with a system of robust striations or ribs, of varying strength and length. The longest end towards the poles, and shorter ones alternate between them. In the specimen described, the long ribs of the epitheca reach the apex, while on the hypotheca, approximately one in two stops around the halfway or second third of the way down this hypotheca.
Three specimens were found in a flint pebble (? Senonian) collected in Paris. A fourth, which appears to belong to the same species, comes from a Senonian flint from the Beynes chalk (SW). In three measurable specimens, the length varies between approximately 60 and 65 μm.
The uncertainty, which cannot be completely resolved with regard to the frontal view, hardly allows for comparison with extant species. However, one can cite, as a relative, Gymnodinium diploconus Schütt (Schiller, 1932, op. cit., p. 353, fig. 359 a-c), which measures 57 to 80 μm, and whose representations, moreover, are not very concordant, present some of the characteristics of Gymnodinium heterocostatum.
But, here again, the strong striations of the membrane of the latter reject any attempt at identification between the two species.