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Dinogymnium cretaceum
From Fensome et al., 2019:
Dinogymnium cretaceum (Deflandre, 1936b, p.164–165, pl.2, figs.1–3) Evitt et al., 1967, p.17–18. Holotype: Deflandre, 1934, figs.9–10; Deflandre, 1935, pl.5, figs.6–7; text-figs.4–5; Deflandre, 1936b, pl.2, figs.1–2. Originally Gymnodinium (Appendix B), subsequently (and now) Dinogymnium. Age: ?Senonian.
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Original description: [Deflandre, 1936b]:
GYMNODINIUM CRETACEUM Deflandre.
Plate II, figs. 1 to 3.
G. DEFLANDRE, C. R. Acad. Sc., CXCIX, 1934, p. 967, figs. 9-10.
Bulletin Biologique, LXIX, 1935, p. 126, figs. 4, 5, and plate V, figs. 6, 7, 8.
Fossil Flagellates, 1936, p. 56, figs. 91, 92.
Holotype: AH 51, Silex S. 8, pebble, Paris.
The epitheca and hypotheca are of approximately equal size. Their shape is broadly conical, with a rounded apex and slightly convex flanks. The transverse groove, very deep, is helical and left-handed, as in all extant species: if we start from the part of the whorl (formed by this groove) closest to the apex, the coiling is to the left, the observer being assumed to be looking at the organism from the apex. The longitudinal groove is represented by a very slightly marked rounded notch on the epitheca, and by an elongated slit that gradually thins out on the hypotheca. The cell is adorned with strong longitudinal ribs, more powerful towards the groove and gradually diminishing towards the poles where they disappear. Some are barely developed and very short; about five or six are visible in the frontal view. The membrane, between the striations, as in the transverse groove, is somewhat granular, as if chafed; but this structure is perhaps secondary. It is light brownish in color. The dimensions of the best-preserved specimen are: length 33 μ, width 21 μ. Of the half-dozen other specimens
massaged in the same flint flake, lengths of 33 to 42 μ can be observed, depending on the position and state of preservation.
It is rather curious to note that seven specimens of this species are gathered in a flake of approximately 2 cubic millimeters, while the examination of more than a hundred flakes, often of much larger size, from the same flint, has only revealed one other specimen, which is, moreover, poorly preserved and identifiable only thanks to knowledge acquired through the study of other specimens.
From a systematic point of view, Gymnodinium cretaceum is not really close to any extant species. It can only be compared to Gymnodinium rhomboides Schütt (Cf. J. Schiller, 1932, p. 406, fig. 426) (1), whose dimensions are similar and whose general shape is also rhomboid. But the transverse groove of G. rhomboides is barely helical, and its ornamentation, formed of broad rounded ribs, is completely different.
Dinogymnium cretaceum (Deflandre, 1936b, p.164–165, pl.2, figs.1–3) Evitt et al., 1967, p.17–18. Holotype: Deflandre, 1934, figs.9–10; Deflandre, 1935, pl.5, figs.6–7; text-figs.4–5; Deflandre, 1936b, pl.2, figs.1–2. Originally Gymnodinium (Appendix B), subsequently (and now) Dinogymnium. Age: ?Senonian.
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Original description: [Deflandre, 1936b]:
GYMNODINIUM CRETACEUM Deflandre.
Plate II, figs. 1 to 3.
G. DEFLANDRE, C. R. Acad. Sc., CXCIX, 1934, p. 967, figs. 9-10.
Bulletin Biologique, LXIX, 1935, p. 126, figs. 4, 5, and plate V, figs. 6, 7, 8.
Fossil Flagellates, 1936, p. 56, figs. 91, 92.
Holotype: AH 51, Silex S. 8, pebble, Paris.
The epitheca and hypotheca are of approximately equal size. Their shape is broadly conical, with a rounded apex and slightly convex flanks. The transverse groove, very deep, is helical and left-handed, as in all extant species: if we start from the part of the whorl (formed by this groove) closest to the apex, the coiling is to the left, the observer being assumed to be looking at the organism from the apex. The longitudinal groove is represented by a very slightly marked rounded notch on the epitheca, and by an elongated slit that gradually thins out on the hypotheca. The cell is adorned with strong longitudinal ribs, more powerful towards the groove and gradually diminishing towards the poles where they disappear. Some are barely developed and very short; about five or six are visible in the frontal view. The membrane, between the striations, as in the transverse groove, is somewhat granular, as if chafed; but this structure is perhaps secondary. It is light brownish in color. The dimensions of the best-preserved specimen are: length 33 μ, width 21 μ. Of the half-dozen other specimens
massaged in the same flint flake, lengths of 33 to 42 μ can be observed, depending on the position and state of preservation.
It is rather curious to note that seven specimens of this species are gathered in a flake of approximately 2 cubic millimeters, while the examination of more than a hundred flakes, often of much larger size, from the same flint, has only revealed one other specimen, which is, moreover, poorly preserved and identifiable only thanks to knowledge acquired through the study of other specimens.
From a systematic point of view, Gymnodinium cretaceum is not really close to any extant species. It can only be compared to Gymnodinium rhomboides Schütt (Cf. J. Schiller, 1932, p. 406, fig. 426) (1), whose dimensions are similar and whose general shape is also rhomboid. But the transverse groove of G. rhomboides is barely helical, and its ornamentation, formed of broad rounded ribs, is completely different.