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Pierceites schizocystis
Pierceites *schizocystis Habib and Drugg, 1987, p.761–762, pl.6, figs.1–6.
Holotype: Habib and Drugg, 1987, pl.6, fig.1; Fensome et al., 1995, fig.1 — p.1769. Age: ?Cenomanian.
Original descriplion: Habib and Drugg, 1987, p. 762
Proximate autocysts with rounded peridinioid outline. Cyst wall thin, ca. 0.5 µm thick. Evidence of pericoels lacking. Apical horn broadly based and tapers smoothly to a rounded apex. Antapical horns usually weakly developed and of unequal length; left horn longer, right horn reduced or occasionally undeveloped. Structural evidence of a cinyulum lacking; its position is inferred in those cysts where the epicyst partially or completely splits from the hypocyst, or where precingular plates dehisce from hypocyst. Sulcus not evident. Except for the archeopyle, evidence of cyst tabulation is lacking in most specimens. However, in other specimens, the epicystal tabulation is expressed by sutural lines of dehiscence defining plate boundaries of the apical, intercalary, and percingular series and by the separation of individual plates, especially in the precingular series. Hypocystal tabulation not evident. Partial tabulation formula is peridiniacean: 4", 3a, 7"". Apical series distinguished by first apical plate (1") which does not extend to the apex; sutural boundary of second apical (2") and fourth apical (4") plates in direct contact in ventral side of apical horn. Intercalary series typically peridiniacean; mid-dorsal second intercalary plate (2a) attenuated, but with the 2a/3" boundary not much shorter than the 2a/4"" boundary. Precingular plates may dehisce individually along cingular margin and from remainder of epicyst. Archeopyle formula 3I. Operculum compound, with each opercular piece corresponding to a plate of the intercalary series; opercular pieces generally separate, but may remain in place. Cyst surface evenly scabrate to finely granulate. Pustules are commonly scattered among granules, but may also be more densely distributed.
Cyst length ranges from 70 to 85 µm; width from 49 to 62 µm. Apical horn ranges from 10 to 16 µm in length; left antapical horn from 5 to 10 µm.
Affinities: Habib and Drugg, 1987, p. 762
Pierceites schizocystis is distinguished by its rounded peridinioid outline, surface ornamentation, inclusion of specimens which possess an epicystal tabulation outlined by suturally deshicing boundaries, and lack of sulcus and cingulum. The species is named after the common splitting of the epicyst. Evitt (1967, pl. 3, fig. 16) illustrated a specimen he labelled Forma Q, from the Cretaceous of South Dakota. It is referable to the genus Pierceites, and is close to P. schizocystis. It differs by its Possession of a distinct cingulum.
Holotype: Habib and Drugg, 1987, pl.6, fig.1; Fensome et al., 1995, fig.1 — p.1769. Age: ?Cenomanian.
Original descriplion: Habib and Drugg, 1987, p. 762
Proximate autocysts with rounded peridinioid outline. Cyst wall thin, ca. 0.5 µm thick. Evidence of pericoels lacking. Apical horn broadly based and tapers smoothly to a rounded apex. Antapical horns usually weakly developed and of unequal length; left horn longer, right horn reduced or occasionally undeveloped. Structural evidence of a cinyulum lacking; its position is inferred in those cysts where the epicyst partially or completely splits from the hypocyst, or where precingular plates dehisce from hypocyst. Sulcus not evident. Except for the archeopyle, evidence of cyst tabulation is lacking in most specimens. However, in other specimens, the epicystal tabulation is expressed by sutural lines of dehiscence defining plate boundaries of the apical, intercalary, and percingular series and by the separation of individual plates, especially in the precingular series. Hypocystal tabulation not evident. Partial tabulation formula is peridiniacean: 4", 3a, 7"". Apical series distinguished by first apical plate (1") which does not extend to the apex; sutural boundary of second apical (2") and fourth apical (4") plates in direct contact in ventral side of apical horn. Intercalary series typically peridiniacean; mid-dorsal second intercalary plate (2a) attenuated, but with the 2a/3" boundary not much shorter than the 2a/4"" boundary. Precingular plates may dehisce individually along cingular margin and from remainder of epicyst. Archeopyle formula 3I. Operculum compound, with each opercular piece corresponding to a plate of the intercalary series; opercular pieces generally separate, but may remain in place. Cyst surface evenly scabrate to finely granulate. Pustules are commonly scattered among granules, but may also be more densely distributed.
Cyst length ranges from 70 to 85 µm; width from 49 to 62 µm. Apical horn ranges from 10 to 16 µm in length; left antapical horn from 5 to 10 µm.
Affinities: Habib and Drugg, 1987, p. 762
Pierceites schizocystis is distinguished by its rounded peridinioid outline, surface ornamentation, inclusion of specimens which possess an epicystal tabulation outlined by suturally deshicing boundaries, and lack of sulcus and cingulum. The species is named after the common splitting of the epicyst. Evitt (1967, pl. 3, fig. 16) illustrated a specimen he labelled Forma Q, from the Cretaceous of South Dakota. It is referable to the genus Pierceites, and is close to P. schizocystis. It differs by its Possession of a distinct cingulum.