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Alterbidinium pseudocirculum
From Fensome et al., 2019:
Alterbidinium pseudocirculum, Vasilyeva in Andreeva-Grigorovich et al., 2011, p.45–46, pl.11, figs.20–24; text-fig.18f ex Williams and Fensome, 2016, p.139.
Holotype: Andreeva-Grigorovich et al., 2011, pl.11, figs.23–24; text-fig. 18f, designated by Williams and Fensome (2016, p.139).
This name was not validly published by Vasilyeva in Andreeva-Grigorovich et al. (2011, p.45–46) since the holotype citation (pl.11, figs.20–24 and text-fig.18f) includes more than one specimen. The holotype was clearly designated in Williams and Fensome (2016), thus validating the name Alterbidinium pseudocirculum.
In the caption to text-fig. 18, the species is referred to as Alterbidinium pseudocingulum.
Age: Danian–Selandian.
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Original description: [Vasilyeva in Andreeva-Grigorovich et al., 2011] (translated from Russian with Google):
Alterbidinium pseudocirculum Vassilyeva sp. nov.
Name. From the Greek ψεῦδος - false, and Latin circulus - round; has a similarity with Alterbidinium circulum, but differs from the latter in a number of features.
Diagnosis. Peridinioid circumcavate elongate-oval cyst of intermediate to large size. Apical horn conical, top rounded off. Left antapical horn usually well developed, right one reduced. Endocyst rounded to oval. Perifragm thin, smooth, transparent. Endophragm thin, more dense, smooth or lightly scabrate. Periarcheopyle hexagonal of intercalary or intercalary-precingular type. Paracingulum poorly defined by flat furrow and low folds. Parasulcus not indicated.
Description: Pericyst is longitudinally elongated, rounded-pentagonal. The epicyst is approximately equal in length to the epicyst. The lateral sides of the epicyst are slightly convex, without bends or "shoulders". The apical horn is moderately elongated, its apex is rounded; sometimes with a short spine. The hypocyst has slightly concave lateral sides, asymmetrical. The antapical horns are of different lengths; the left antapical horn is well developed, pointed, the right one is significantly reduced. The apex of the right horn is smoothed, rounded. The endocyst is almost round, sometimes rounded-oval, large, occupies a central position in the cell. The periphragm is thin, transparent, smooth, dense, not crushed into folds. The endophragm is thin, smooth or unclearly tuberculate, slightly denser and darker than the periphragm. Sometimes inclusions of organic material in the form of large grains are found on the endophragm. The pericoel is well defined, not wide, occasionally narrowing significantly in the area of the cingulum and lateral parts of the pericyst, so that the membranes practically touch. The periarchaeopile is slightly elongated, rounded-hexagonal, the type is intercalary or combined intercalary-precingular. The perioperculum is attached. The endoarchaeopile is rounded-hexagonal. The endoperculum is attached. The paracingulum is expressed by a slightly raised, weakly concave wide groove and a thin, short, single or double fold of the periphragm. The parasulcus is not expressed.
Holotype. Table XI, 20-24; rice. 18, e. Rev. Wed. Saltanovo 46a-04.
Location. Saltanovo outcrop, Lyalya River, Talitskaya (Ivdelskaya) suite (Sverdlovsk region, Serovsky district, Saltanovo village).
Dimensions (µm). Holotype: pericyst length 71.2; pericyst width 45; endocyst diameter 45.0-44.2. Other specimens (3 specimens): pericyst length 75.2-69.4; pericyst width 50.0-43.2; endocyst length 46.2-43.4; endocyst width 45.2-43.0.
Comparison. Differs from the morphologically close species Alterbidinium circulum by a more elongated pericyst shape, the structure of the antapical horns, the shape of the hypocyst (the characteristic for A. circulum "notch" on the side of the shortened antapical horn is absent), the shape of the epicyst (Alterbidinium pseudocirculum sp. nov. lacks "shoulders"), a narrower pericoel, and a significantly smoother shape of the paracingulum.
Distribution. Russia, Middle Trans-Urals, Talitskaya, Ivdelskaya suites. Paleocene (Danian-Zealandian).
Alterbidinium pseudocirculum, Vasilyeva in Andreeva-Grigorovich et al., 2011, p.45–46, pl.11, figs.20–24; text-fig.18f ex Williams and Fensome, 2016, p.139.
Holotype: Andreeva-Grigorovich et al., 2011, pl.11, figs.23–24; text-fig. 18f, designated by Williams and Fensome (2016, p.139).
This name was not validly published by Vasilyeva in Andreeva-Grigorovich et al. (2011, p.45–46) since the holotype citation (pl.11, figs.20–24 and text-fig.18f) includes more than one specimen. The holotype was clearly designated in Williams and Fensome (2016), thus validating the name Alterbidinium pseudocirculum.
In the caption to text-fig. 18, the species is referred to as Alterbidinium pseudocingulum.
Age: Danian–Selandian.
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Original description: [Vasilyeva in Andreeva-Grigorovich et al., 2011] (translated from Russian with Google):
Alterbidinium pseudocirculum Vassilyeva sp. nov.
Name. From the Greek ψεῦδος - false, and Latin circulus - round; has a similarity with Alterbidinium circulum, but differs from the latter in a number of features.
Diagnosis. Peridinioid circumcavate elongate-oval cyst of intermediate to large size. Apical horn conical, top rounded off. Left antapical horn usually well developed, right one reduced. Endocyst rounded to oval. Perifragm thin, smooth, transparent. Endophragm thin, more dense, smooth or lightly scabrate. Periarcheopyle hexagonal of intercalary or intercalary-precingular type. Paracingulum poorly defined by flat furrow and low folds. Parasulcus not indicated.
Description: Pericyst is longitudinally elongated, rounded-pentagonal. The epicyst is approximately equal in length to the epicyst. The lateral sides of the epicyst are slightly convex, without bends or "shoulders". The apical horn is moderately elongated, its apex is rounded; sometimes with a short spine. The hypocyst has slightly concave lateral sides, asymmetrical. The antapical horns are of different lengths; the left antapical horn is well developed, pointed, the right one is significantly reduced. The apex of the right horn is smoothed, rounded. The endocyst is almost round, sometimes rounded-oval, large, occupies a central position in the cell. The periphragm is thin, transparent, smooth, dense, not crushed into folds. The endophragm is thin, smooth or unclearly tuberculate, slightly denser and darker than the periphragm. Sometimes inclusions of organic material in the form of large grains are found on the endophragm. The pericoel is well defined, not wide, occasionally narrowing significantly in the area of the cingulum and lateral parts of the pericyst, so that the membranes practically touch. The periarchaeopile is slightly elongated, rounded-hexagonal, the type is intercalary or combined intercalary-precingular. The perioperculum is attached. The endoarchaeopile is rounded-hexagonal. The endoperculum is attached. The paracingulum is expressed by a slightly raised, weakly concave wide groove and a thin, short, single or double fold of the periphragm. The parasulcus is not expressed.
Holotype. Table XI, 20-24; rice. 18, e. Rev. Wed. Saltanovo 46a-04.
Location. Saltanovo outcrop, Lyalya River, Talitskaya (Ivdelskaya) suite (Sverdlovsk region, Serovsky district, Saltanovo village).
Dimensions (µm). Holotype: pericyst length 71.2; pericyst width 45; endocyst diameter 45.0-44.2. Other specimens (3 specimens): pericyst length 75.2-69.4; pericyst width 50.0-43.2; endocyst length 46.2-43.4; endocyst width 45.2-43.0.
Comparison. Differs from the morphologically close species Alterbidinium circulum by a more elongated pericyst shape, the structure of the antapical horns, the shape of the hypocyst (the characteristic for A. circulum "notch" on the side of the shortened antapical horn is absent), the shape of the epicyst (Alterbidinium pseudocirculum sp. nov. lacks "shoulders"), a narrower pericoel, and a significantly smoother shape of the paracingulum.
Distribution. Russia, Middle Trans-Urals, Talitskaya, Ivdelskaya suites. Paleocene (Danian-Zealandian).