Sterol Distribution in the Genus Heterocapsa (Pyrrhophyta) 1

The sterol composition of seven strains of marine peridinioid dinoflagellates comprising the four known species of Heterocapsa Stein was examined by gas chromatography‐mass spectrometry to determine the utility of these compounds in systematics. Cholest‐5‐en‐3β‐ol (cholesterol), 24‐methyl‐cholest‐5‐en‐3β‐ol (24‐methylcholesterol), 4α,24(S)‐dimethyl‐5α‐cholestan‐3β‐ol (4,24‐dimethylcholestanol), 4α,23,24(R)‐trimethyl‐5α‐cholest‐22‐en‐3β‐ol (dinosterol), 4α,23ξ,24ξ‐trimethyl‐5α‐cholestan‐3β‐ol (dihydrodinosterol), and an unknown sterol were detected. Sterol composition does not vary significantly from species to species within the genus Heterocapsa and thus cannot be used for species differentiation. Sterols may, however, have value in defining the properties of dinoflagellate taxa above the family level. Over the course of the growth curve for Heterocapsa niei (Loeblich) Morrill & Loeblich 4,24‐dimethylcholestanol and dinosterol covaried, suggesting that 4,24‐dimethylcholestanol is converted into dinosterol by a previously proposed bioalkylation scheme.