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Aprobolocysta cornuta
Aprobolocysta cornuta, Pestchevitskaya, 2006, p. S642, pl. 7, fig.16; text-fig.3D.
Holotype: Pestchevitskaya, 2006, pl.7, fig.16.
Locality: Western Siberia (middle course of the Ob River), Gorshkovskaya 1017 borehole, 2629.7– 2442.6 m, Upper Hauterivian–Lower Barremian.
Age: late Hauterivian–early Barremian.
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Original description: [Pestchevitskaya, 2006]:
Diagnosis:
Cyst elongate oval, proximate, bilayered, with apical horn; apex longer and more tapering than antapex; endophragm thicker, with small granules, periphragm thin and transparent; no paratabulation apparent except for archeopyle margin; archeopyle apical.
Description:
(Fig. 3D). The cyst is proximate, bilayered, and elongated oval or ovate. The hypocyst is smaller in height, but wider than the epicyst. The apex is rounded. There is a horn of a medium length in the antapical area. It is narrow on the endocyst and wide on the pericyst. The endophragm is relatively dense and finely granulate. The periphragm is thinner, transparent, and folded. The largest fold girdles the cyst in the cingular area like a “skirt.” In precingular area, the endophragm and periphragm may be closely appressed to each other or form a small pericoel, which becomes significantly wider toward the apex and antapex. In the apical area, the pericoel is elongate reproducing the outlines of the horn on the endocyst. The paratabulation is visible only in the operculum detachment line. The position of the paracingulum is indicated by a broad fold.
The archeopyle is apical.
Dimensions (µm):
the length of the dinocyst is 95–104 (without operculum 75–79); the width is 45–50; the length of the endocyst is 74–79, the width is 35–37; the length of the apical horn on the periphragm is 28–30, the width is 14–16 near the base and 5 at the distal side; the length of the apical horn on the endophragm is 14–15, the width is 4–5 near the base and 2 distally; the width of the pericoel in the antapical area is 10–15.
Variability: The sizes of the cyst and pericoel vary slightly.
Affinities/Comparison:
A. cornuta differs from the closest species A. eilema (Duxbury, 1977) in the presence of an apical horn, and in having a finely granulate endophragm. A. alata Backhouse differs in the presence of antapical horns and paratabulation that is expressed not only in the archeopyle, but also in the position of the periphragm folds (Backhouse, 1987).
Holotype: Pestchevitskaya, 2006, pl.7, fig.16.
Locality: Western Siberia (middle course of the Ob River), Gorshkovskaya 1017 borehole, 2629.7– 2442.6 m, Upper Hauterivian–Lower Barremian.
Age: late Hauterivian–early Barremian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Pestchevitskaya, 2006]:
Diagnosis:
Cyst elongate oval, proximate, bilayered, with apical horn; apex longer and more tapering than antapex; endophragm thicker, with small granules, periphragm thin and transparent; no paratabulation apparent except for archeopyle margin; archeopyle apical.
Description:
(Fig. 3D). The cyst is proximate, bilayered, and elongated oval or ovate. The hypocyst is smaller in height, but wider than the epicyst. The apex is rounded. There is a horn of a medium length in the antapical area. It is narrow on the endocyst and wide on the pericyst. The endophragm is relatively dense and finely granulate. The periphragm is thinner, transparent, and folded. The largest fold girdles the cyst in the cingular area like a “skirt.” In precingular area, the endophragm and periphragm may be closely appressed to each other or form a small pericoel, which becomes significantly wider toward the apex and antapex. In the apical area, the pericoel is elongate reproducing the outlines of the horn on the endocyst. The paratabulation is visible only in the operculum detachment line. The position of the paracingulum is indicated by a broad fold.
The archeopyle is apical.
Dimensions (µm):
the length of the dinocyst is 95–104 (without operculum 75–79); the width is 45–50; the length of the endocyst is 74–79, the width is 35–37; the length of the apical horn on the periphragm is 28–30, the width is 14–16 near the base and 5 at the distal side; the length of the apical horn on the endophragm is 14–15, the width is 4–5 near the base and 2 distally; the width of the pericoel in the antapical area is 10–15.
Variability: The sizes of the cyst and pericoel vary slightly.
Affinities/Comparison:
A. cornuta differs from the closest species A. eilema (Duxbury, 1977) in the presence of an apical horn, and in having a finely granulate endophragm. A. alata Backhouse differs in the presence of antapical horns and paratabulation that is expressed not only in the archeopyle, but also in the position of the periphragm folds (Backhouse, 1987).