From Fensome et al., 2019:
Triblastula nuda Wetzel, 1961, p.340, pl.2, fig.2.
Holotype: Wetzel, 1961, pl.2, fig.2.
Originally Triblastula, subsequently Hystrichosphaeropsis.
Taxonomic senior synonym: Triblastula (as and now Hystrichosphaeropsis) quasicribrata, according to Marheinecke (1992, p.44).

Locus typicus: Baltic Cretaceous flintstones
Stratum typicum: Erratic, ?Late Cretaceous

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Original diagnosis: O. Wetzel, 1961, p.340
Central portion spheroidal, smooth, without spines. Usually only one of the "pole-caps" has a terminal point (apex); the other is more cuboidal or cylindrical, narrowing somewhat at the end. The caps often have four longitudinal striations, which may indicate the corners of the broad areas or fields of the shell. The circular bases of the two caps together appear as a narrow pair of parallel lines, and may represent the equatorial "girdle" of a true dinoflagellate. "Pylomes" are apparently not rare.
Dimensions: 96 x 48 µm; 100 x 45 µm.