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Endoceratium immarinum
Genus Endoceratium Vozzhennikova, 1965
Endoceratium immarinum Razumkova, sp. nov.
Plate 13, figs. 1–15
Etymology. From the Latin in (non) and marinus (marine).
Holotype. GEOR, no. K22 23/339 3p; southwest of Western Siberia, borehole A3, sample 339, depth of 854.52 m; upper part of the Vikulovo Formation; designated herein; Pl. 13, fig. 4.
Diagnosis. Intermediate ceratioid cyst with four well developed horns: one apical, one antapical, one lateral, and one postcingular; cyst two walled, circumcavate; paratabulation indicated by cingulum; archeopyle apical (type tA).
Description (Figs. 3b, 4). The cyst is intermediate, ceratioid, dorsoventrally compressed, with well-developed apical, left lateral, right postcingular, and one anatapical horns. The cyst is two walled, circumcavate. The endocyst is rhomboid, with convex sides and asymmetrical. The apical horn is narrow, longer than the others. The lateral horns are in the form of wide swellings and the right lateral process is longer. The antapical horn is conical, relatively long. The pericyst repeats the shape of the endocyst, but has longer processes. The apical horn is narrow, longer than the other horns, and is shaped as the antapical horn. The left lateral horn is well developed, with small pre and postcingular extensions, usually rounded, less commonly triangular (Pl. 13, fig. 3). The right postcingular process is relatively long, conical, and sometimes comparable with the antapical horn in size and shape, but can also be shorter. All horn terminations are rounded. The endocyst is smooth; the pericyst is usually smooth, but can be scabrous. Both walls are very thin. The paratabulation is most commonly expressed by a cingulum, which can be indicated by indentation of the lateral horns and weakly or clearly visible trans verse ribs (Pl. 13, fig. 5). The archeopyle is apical, of tA type; the archeopyle suture is zigzag is rarely visible (Pl. 13, figs. 1–3). The operculum is attached ventrally, rarely broken off.
Remarks. The pericyst is very thin, hence, it is easily folded, and the postcingular horn can be flexed toward the antapical horn (Fig. 3b). This should be noted, because the flexed horn can give an erroneous impression of the cyst morphology (e.g., it would be incorrect to infer that the cyst has two antapical horns) (Pl. 13, fig. 12).
Dimensions, μm. Length, 72 (84) 98; width, 38 (48) 56; apical horn length, 24 (35) 40; apical pericoel length, 7–10; left lateral horn length, 5–13, more commonly, 10; length of pre and postcingular projections on it, 1–3; right lateral horn, 2–3 μm long;
postcingular horn length, 5 (16) 24; antapical horn length, 13 (19) 29.
Variability. The characters are relatively stable.
Comparison. The new species differs from all congeners in the presence of the well developed lateral horn and in the more intricate shape of the endocyst, whereas in other species of Endoceratium, it is rather rounded triangular. E. dettmannae Cookson and Hughes, 1964, which also has an almost rhomboid outline, but with convex sides and in places scabrous surface, is the most similar. The pericyst of E. dettmannae very precisely follows the shape of the endocyst, and all the projections are commensurable and relatively short. A relatively short band ornamented with small indentations is visible on the ventral and dorsal surfaces in the lateral region of the cyst.
Ma t e r i a l. Twenty nine well preserved specimens; Russia, Western Siberia, upper part of the Vikulovo Formation, Middle–Upper Aptian; borehole A1, interval 893.02–825.07 m; borehole A3, interval 899.63–854.52 m; borehole B4, interval 868.4–835.1 m; borehole B3, interval 886.25–845.3 m.
Endoceratium immarinum Razumkova, sp. nov.
Plate 13, figs. 1–15
Etymology. From the Latin in (non) and marinus (marine).
Holotype. GEOR, no. K22 23/339 3p; southwest of Western Siberia, borehole A3, sample 339, depth of 854.52 m; upper part of the Vikulovo Formation; designated herein; Pl. 13, fig. 4.
Diagnosis. Intermediate ceratioid cyst with four well developed horns: one apical, one antapical, one lateral, and one postcingular; cyst two walled, circumcavate; paratabulation indicated by cingulum; archeopyle apical (type tA).
Description (Figs. 3b, 4). The cyst is intermediate, ceratioid, dorsoventrally compressed, with well-developed apical, left lateral, right postcingular, and one anatapical horns. The cyst is two walled, circumcavate. The endocyst is rhomboid, with convex sides and asymmetrical. The apical horn is narrow, longer than the others. The lateral horns are in the form of wide swellings and the right lateral process is longer. The antapical horn is conical, relatively long. The pericyst repeats the shape of the endocyst, but has longer processes. The apical horn is narrow, longer than the other horns, and is shaped as the antapical horn. The left lateral horn is well developed, with small pre and postcingular extensions, usually rounded, less commonly triangular (Pl. 13, fig. 3). The right postcingular process is relatively long, conical, and sometimes comparable with the antapical horn in size and shape, but can also be shorter. All horn terminations are rounded. The endocyst is smooth; the pericyst is usually smooth, but can be scabrous. Both walls are very thin. The paratabulation is most commonly expressed by a cingulum, which can be indicated by indentation of the lateral horns and weakly or clearly visible trans verse ribs (Pl. 13, fig. 5). The archeopyle is apical, of tA type; the archeopyle suture is zigzag is rarely visible (Pl. 13, figs. 1–3). The operculum is attached ventrally, rarely broken off.
Remarks. The pericyst is very thin, hence, it is easily folded, and the postcingular horn can be flexed toward the antapical horn (Fig. 3b). This should be noted, because the flexed horn can give an erroneous impression of the cyst morphology (e.g., it would be incorrect to infer that the cyst has two antapical horns) (Pl. 13, fig. 12).
Dimensions, μm. Length, 72 (84) 98; width, 38 (48) 56; apical horn length, 24 (35) 40; apical pericoel length, 7–10; left lateral horn length, 5–13, more commonly, 10; length of pre and postcingular projections on it, 1–3; right lateral horn, 2–3 μm long;
postcingular horn length, 5 (16) 24; antapical horn length, 13 (19) 29.
Variability. The characters are relatively stable.
Comparison. The new species differs from all congeners in the presence of the well developed lateral horn and in the more intricate shape of the endocyst, whereas in other species of Endoceratium, it is rather rounded triangular. E. dettmannae Cookson and Hughes, 1964, which also has an almost rhomboid outline, but with convex sides and in places scabrous surface, is the most similar. The pericyst of E. dettmannae very precisely follows the shape of the endocyst, and all the projections are commensurable and relatively short. A relatively short band ornamented with small indentations is visible on the ventral and dorsal surfaces in the lateral region of the cyst.
Ma t e r i a l. Twenty nine well preserved specimens; Russia, Western Siberia, upper part of the Vikulovo Formation, Middle–Upper Aptian; borehole A1, interval 893.02–825.07 m; borehole A3, interval 899.63–854.52 m; borehole B4, interval 868.4–835.1 m; borehole B3, interval 886.25–845.3 m.