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Alterbidinium emulatum
From Fensome et al., 2019:
Alterbidinium emulatum, Mao Shaozhi and Norris, 1988, p.41–42, pl.9, figs.1–2; text-fig.12.
Holotype: Mao Shaozhi and Norris, 1988, pl.9, fig.1.
Age: Late Cretaceous.
Locus typicus: Kukebai Formation, Wuluokeqiate section, China
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Original description: [Mao Shaozhi and Norris, 1988, p. 41]:
Diagnosis:
Cyst proximate, circumcavate, elongated pentagonal with straight or convex sides. Both apical and left antapical horns short with broad bases. Endoblast subspherical to oval, relatively large, close to periphragm laterally, resulting typically in two narrow ambital pericoels.
Archeopyle intercalary, type (I), attenuated hexa 2a. Transverse archeopyle index (AI) 0.35 to 0.47.
Description:
Cyst laterally asymmetrical, ambitus biconical.
Apical horn short, bluntly pointed, formed by tapering of two sides of epitract; a small circular thickening, about 2 to 3 µm diameter, usually at top. Left antapical horn pointed with very broad base; right one either poorly developed or, more often, undeveloped. Shape of endoblast approximately paralleling that of periblast (see Text-Fig. 12); sometimes endoblast protruding to base of apical and left antapical horns. Periphragm thin and granulate, endophragm smooth.
Cingulum usually present, 4 to 6 µm wide, slightly levorotatory, delineated by wavy folds or low denticulate ridges.
Sulcus restricted to hypotract.
Archeopyle on periphragm attenuated hexa, with hexagonal 2a, relatively longer anterior lateral sides (H2 and H6), and reduced posterior lateral sides (H3 and H5); the anterior margin (H,) much shorter than posterior margin (H4), giving hexagonal archeopyle a superficially triangular shape. Archeopyle on endophragm not clearly discernible.
Dimensions:
Overall: length 61 to 80 µm (holotype 75 µm), width 40 to 50 µm (holotype 46 µm); endoblast: length 36 to 60 µm (holotype 50 µm), width 30 to 45 µm (holotype 42 µm).
Affinities:
Alterbidinium emulatum resembles A. acutulum and lsabelidinium acuminatum. It differs from A. acutulum in having a cyst that is plump, with two sides of the epitract straight or convex, and apical and left antapical horns that are much shorter. I. acuminatum differs from A. emulatum in possessing (I) an endoblast of smaller size, located more centrally in the cyst, and a circular ambitus slightly pointed towards the apex and (2) a relatively wide pericoel between the endophragm and periphragm. A. emulatum also shows some similarity to Deflandrea psilata, but the latter is smaller (48 to 50 µm).
Alterbidinium emulatum, Mao Shaozhi and Norris, 1988, p.41–42, pl.9, figs.1–2; text-fig.12.
Holotype: Mao Shaozhi and Norris, 1988, pl.9, fig.1.
Age: Late Cretaceous.
Locus typicus: Kukebai Formation, Wuluokeqiate section, China
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Original description: [Mao Shaozhi and Norris, 1988, p. 41]:
Diagnosis:
Cyst proximate, circumcavate, elongated pentagonal with straight or convex sides. Both apical and left antapical horns short with broad bases. Endoblast subspherical to oval, relatively large, close to periphragm laterally, resulting typically in two narrow ambital pericoels.
Archeopyle intercalary, type (I), attenuated hexa 2a. Transverse archeopyle index (AI) 0.35 to 0.47.
Description:
Cyst laterally asymmetrical, ambitus biconical.
Apical horn short, bluntly pointed, formed by tapering of two sides of epitract; a small circular thickening, about 2 to 3 µm diameter, usually at top. Left antapical horn pointed with very broad base; right one either poorly developed or, more often, undeveloped. Shape of endoblast approximately paralleling that of periblast (see Text-Fig. 12); sometimes endoblast protruding to base of apical and left antapical horns. Periphragm thin and granulate, endophragm smooth.
Cingulum usually present, 4 to 6 µm wide, slightly levorotatory, delineated by wavy folds or low denticulate ridges.
Sulcus restricted to hypotract.
Archeopyle on periphragm attenuated hexa, with hexagonal 2a, relatively longer anterior lateral sides (H2 and H6), and reduced posterior lateral sides (H3 and H5); the anterior margin (H,) much shorter than posterior margin (H4), giving hexagonal archeopyle a superficially triangular shape. Archeopyle on endophragm not clearly discernible.
Dimensions:
Overall: length 61 to 80 µm (holotype 75 µm), width 40 to 50 µm (holotype 46 µm); endoblast: length 36 to 60 µm (holotype 50 µm), width 30 to 45 µm (holotype 42 µm).
Affinities:
Alterbidinium emulatum resembles A. acutulum and lsabelidinium acuminatum. It differs from A. acutulum in having a cyst that is plump, with two sides of the epitract straight or convex, and apical and left antapical horns that are much shorter. I. acuminatum differs from A. emulatum in possessing (I) an endoblast of smaller size, located more centrally in the cyst, and a circular ambitus slightly pointed towards the apex and (2) a relatively wide pericoel between the endophragm and periphragm. A. emulatum also shows some similarity to Deflandrea psilata, but the latter is smaller (48 to 50 µm).