Stenophagy as a Pathway for the Occurrence of Unique Coral Fatty Acid Biomarkers in Higher Branches of the Marine Tree of Life: The Nudibranch Armina maculata Case

Tetracosapolyenoic fatty acids (TPA), namely tetracosapentaenoic (24:5 n -6) and tetracosahexaenoic (24:6 n -3) acids, are chemotaxonomic biomarkers of octocorals (Cnidaria, Octocorallia) in the marine environment. The present study confirms the occurrence of TPA on a marine non-cnidarian taxon, the nudibranch mollusc Armina maculata . This discovery is explained by the specialized feeding regime (stenophagy) of this sea slug that preys upon the octocoral Veretillum cynomorium . The prevalence of 24:5 n -6 and 24:6 n -3 in the body of A. maculata was demonstrated through the analysis of specimens starved for 30 days in captivity. Since the time frame is superior to the residence time of ingested octocorals, the present findings provide empirical evidence that the reported TPA are allocated from nudibranch tissues. Here we found support for previous claims that the presence of TPA in the marine tree of life is not restricted to its lower branches, as stenophagous trophic interactions may allow its transfer to or posterior biosynthesis in more evolved taxa.