Fatty acids in crinoidea and ophiuroidea: Occurrence of all‐cis‐6,9,12,15,18,21‐tetracosahexaenoic acid

The fatty acid compositions of lipids from two species of Crinoidea and two species of Ophiuroidea have been investigated with open‐tubular gas chromatography. About 5–10% of tetracosahexaenoic acid was found in total fatty acids from all the samples, and the structure was determined as all‐cis‐6,9,12,15,18,21‐tetracosahexaenoic acid [24∶6(n−3)] by13C‐NMR of the methyl esters and mass spectrometric analyses of the methyl esters, the pyrrolidides and the ozonolysis products. The 24∶6(n−3) was concentrated in the polar lipids rather than neutral lipids. The n−3 hexaenoic structure suggested chain elongation of 22∶6(n−3) as the source. The 5‐olefinic acids (5−18∶1, 5−20∶1, 5,11‐ and 5,13−20∶2) were low in Crinoidea (0.2–1.3%) but were present in higher levels (2.5–5.2%) in Ophiuroidea. Polyunsaturated acids found other than 24∶6(n−3) were 20∶4(n−6), 20∶5(n−3) and 22∶6(n−3) as major components and 16∶3(n−3), 18∶2(n−6), 18∶3(n−6), 18∶3(n−3), 18∶4(n−3), 20∶2(n−9), 20∶2(n−6), 20∶3(n−6), 20∶3(n−3), 21∶5(n−3) and 22∶5(n−3) as minor components in all the samples.