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Trithyrodinium pentagonum

From Fensome et al., 2019:
Trithyrodinium pentagonum May, 1980, p.87–88, pl.10, figs.13–14.
Holotype: May, 1980, pl.10, figs.13–14.
NOW Pierceites. Originally Trithyrodinium, subsequently (and now) Pierceites.
Locus typicus: Atlantic Highlands, New Jersey
Stratum typicum: Maastrichtian

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Original description: May, 1980, p.87-88
Cyst single layered autoblast, pentagonal in dorso-ventral outline; dorso-ventrally flattened; tapering apically from cingulum in near linear fashion, deviating at apex to form short, rounded apical horn; tapering antapically from cingulum with slightly concave sides to broadly truncated antapex bearing 2 short antapical horns. Apical horn relatively short (up to 19 µm long), tapering, distally rounded. Left antapical horn relatively short (up to 15 µm long), broadly tapering, V-shaped, blunt-tipped. Right antapical horn short (up to 5 µm long), broad, rounded protrusion. Outline between antapical horns concave and slanting downward to left antapical horn. Autophragm faintly granular to microrugulate; nontabulated. Cingulum slightly levorotatory, ca. 1/2 cingulum width offset, visible mainly dorsally and ventrally, but generally not laterally; formed of 2 parallel folds in autophragm. Sulcus shallow; extends nearly vertically from between terminal ends of cingulum to antapex, intersecting antapex between antapical horns. Archeopyle intercalary (Type 3I); opercular pieces (la, 2a, and 3a plate equivalents) generally in place, but don"t appear attached; 2a plate equivalent hexagonal in outline; la and 3a pentagonal.
Discussion: Characteristic features of T. pentagonum are the pentagonal outline, single wall layer, intercalary archeopyle (Type 3I), and broad blunt antapical processes.
Dimensions: Holotype--L x W, 67 x 49 µm, apical horn length 9 µm, left antapical horn length 8 µm. Observed range (20 specimens measured): length 62-87 µm, width 50-62 µm, apical horn length 9-10 µm, left antapical horn length 2-15 µm, right antapical horn length 3-5 µm. Wall layer, less than 1 µm thick.

Affinities:
May, 1980, p.88: T. pentagonum is dissimilar from T. evittii Drugg 1967 by lacking a distinct endoblast and anterior and posterior pericoels. It is dissimilar from T. fragile Davey 1969 by possessing cingulum and sulcus in some specimens, and in being single layered.
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