THE LIPID COMPOSITION OF THORACOSPHAERA HEIMII: EVIDENCE FOR INCLUSION IN THE DINOPHYCEAE 1

The fatty acid, sterol and chlorophyll composition of the calcified, unicellular alga Thoracosphaera heimii (Lohmann) Kamptner are reported. The presence of 4,23,24‐termethyl‐5α‐cholest‐22E‐en‐3β‐ol (dinosterol), 4,23,24‐trimethyl‐5α‐cholest‐22E‐en‐3‐one (dinosterone) and the predominance of C18, C20 and C22 unsaturated fatty acids, including the acid 18:5ω3, indicates that T. heimii is a dinoflagellate. The fatty acid: sterol ratio (1.3), is typical of dinoflagellates. The geochemical significance of dinosterone, the high relative concentration of 4‐desmethyl‐5α‐stanols and the role of 23‐methyl‐5α‐cholest‐22E‐en‐3β‐ol in the biosynthesis of dinosterol in T. heimii are also discussed.

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