Important polyunsaturated fatty acid of the marine food chain that serves as a precursor for the prostaglandin-3 and thromboxane-3 families. It differs from arachidonic acid (the eicosatetraenoic acid that is a precursor for the prostaglandin and thromboxane-2 families) by the extra double bond between the third and fourth carbons from the “methyl end” of the molecule. Antilipemic.