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Scriniodinium torulosum
From Fensome et al., 2019:
Scriniodinium? torulosum (Deflandre, 1943, p.504–505, pl.17, figs.7–8; text-figs.17–25) Lentin and Williams, 1973, p.124. Holotype: Deflandre, 1943, pl.17, figs.7–8; text-figs.17–20; Jan du Chêne et al., 1986a, pl.104, figs.5–6. Originally Gymnodinium (Appendix B), subsequently (and now) Scriniodinium?. Questionable assignment: Lentin and Williams (1973, p.124). Stover and Evitt (1978, p.188) suggested that this species represents acritarchs; however, Riding and Fensome (2002, p.19) considered it to represent dinoflagellates, albeit as a questionable species of Scriniodinium. Age: Senonian.
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Original description, Deflandre 1943: Gymnodinium torulosum n. sp. (Fig. 17 a 25 et Pl. XVII, fig. 7, 8.)
Holotype: AR 37. Flint (Senonian) S. 140, Saint-Leu-la-Forêt (Seine-et-Oise).
Paratypes: AR 36, AR 38, AR 39, same provenance.
Unlike the other flint Gymnodinium species I have observed, whose membrane is apparently quite robust and very firm in outline, this new form is extremely transparent and difficult to study. The four specimens encountered so far appear to be encysted, as are most of the Jurassic Gymnodinium I have described from the Oxfordian marls of Villiers-sur-Mer. The cyst is more or less regularly ellipsoidal. Its outline is the most visible feature of the cell, due to the thickness of the slightly tinted, light brownish membrane. The overall outline of the cell membrane is hexagonal with rounded corners. The epithelium and the hypotherium are perceptibly equal and shaped like a truncated cone with slightly concave sides. The transverse, helical sulcus is extremely narrow in its inner part; its two lips form two kinds of broad ridges, the median optical section of which is rounded. Similar toric ridges, bordered by an internal hyaline membrane (?), of indistinct outline, occupy the two poles of the organism, themselves slightly depressed towards their center. Furthermore, the cell surface shows some shadows (Figs. 18, 21, 24) that appear to delineate lighter areas, although this does not suggest tabulation. In the holotype and one of the paratypes, one edge of the longitudinal groove is very noticeable, which also allowed for the reconstruction of the true appearance (Fig. 19) of the ventral surface, observed by transparency. Finally, one of the specimens, which is shown in an oblique polar view, suggests that the pole may be quadrangular, something that the well-maintained frontal views do not allow us to discern, especially due to their transparency.
The cell measures 27 to 28 µm long and 24 to 25 µm wide; the paratype in Figure 21 µm appears to be positioned slightly to the side, indicating that the cell must be slightly compressed and have an elliptical cross-section.
This lengthy description, though still somewhat obscure, nevertheless allows, together with the provided illustrations, for a precise understanding of this curious, highly characteristic, and easily recognizable species. Its great transparency is the only obstacle to its identification, an obstacle to which I wish to draw particular attention. None of the current marine species presents a silhouette comparable to that of G. torulosum, whose general shape, particularly the rounded character of the lips of the transverse groove, is more readily found in various extant freshwater Gymnodinium species, such as G. mirabile PENARD or G. carinatum Schilling.
Scriniodinium? torulosum (Deflandre, 1943, p.504–505, pl.17, figs.7–8; text-figs.17–25) Lentin and Williams, 1973, p.124. Holotype: Deflandre, 1943, pl.17, figs.7–8; text-figs.17–20; Jan du Chêne et al., 1986a, pl.104, figs.5–6. Originally Gymnodinium (Appendix B), subsequently (and now) Scriniodinium?. Questionable assignment: Lentin and Williams (1973, p.124). Stover and Evitt (1978, p.188) suggested that this species represents acritarchs; however, Riding and Fensome (2002, p.19) considered it to represent dinoflagellates, albeit as a questionable species of Scriniodinium. Age: Senonian.
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Original description, Deflandre 1943: Gymnodinium torulosum n. sp. (Fig. 17 a 25 et Pl. XVII, fig. 7, 8.)
Holotype: AR 37. Flint (Senonian) S. 140, Saint-Leu-la-Forêt (Seine-et-Oise).
Paratypes: AR 36, AR 38, AR 39, same provenance.
Unlike the other flint Gymnodinium species I have observed, whose membrane is apparently quite robust and very firm in outline, this new form is extremely transparent and difficult to study. The four specimens encountered so far appear to be encysted, as are most of the Jurassic Gymnodinium I have described from the Oxfordian marls of Villiers-sur-Mer. The cyst is more or less regularly ellipsoidal. Its outline is the most visible feature of the cell, due to the thickness of the slightly tinted, light brownish membrane. The overall outline of the cell membrane is hexagonal with rounded corners. The epithelium and the hypotherium are perceptibly equal and shaped like a truncated cone with slightly concave sides. The transverse, helical sulcus is extremely narrow in its inner part; its two lips form two kinds of broad ridges, the median optical section of which is rounded. Similar toric ridges, bordered by an internal hyaline membrane (?), of indistinct outline, occupy the two poles of the organism, themselves slightly depressed towards their center. Furthermore, the cell surface shows some shadows (Figs. 18, 21, 24) that appear to delineate lighter areas, although this does not suggest tabulation. In the holotype and one of the paratypes, one edge of the longitudinal groove is very noticeable, which also allowed for the reconstruction of the true appearance (Fig. 19) of the ventral surface, observed by transparency. Finally, one of the specimens, which is shown in an oblique polar view, suggests that the pole may be quadrangular, something that the well-maintained frontal views do not allow us to discern, especially due to their transparency.
The cell measures 27 to 28 µm long and 24 to 25 µm wide; the paratype in Figure 21 µm appears to be positioned slightly to the side, indicating that the cell must be slightly compressed and have an elliptical cross-section.
This lengthy description, though still somewhat obscure, nevertheless allows, together with the provided illustrations, for a precise understanding of this curious, highly characteristic, and easily recognizable species. Its great transparency is the only obstacle to its identification, an obstacle to which I wish to draw particular attention. None of the current marine species presents a silhouette comparable to that of G. torulosum, whose general shape, particularly the rounded character of the lips of the transverse groove, is more readily found in various extant freshwater Gymnodinium species, such as G. mirabile PENARD or G. carinatum Schilling.