Limit of change in unsaturation index of fatty acid composition of phospholipids at adaptation of molluscs to biogenic and abiogenic environmental factors

Comparative study of fatty acid composition of total phospholipids, as well as of phosphatidylcholine and phosphatidylethanolamine from hepatopancreas and leg muscle was carried out on several representatives of gastropod molluscs (Gastropoda) and on the bivalve mussel Mytilus edulus (Bivalvia). The objects of our study were marine littorins Littorina saxsatilis adapted to different temperature conditions of White Sea and Barents Sea, the freshwater lymnaea Lymnaea stagnalis infested by Trematoda, and mussels from the White and Black Seas. It was shown that depending on the existence conditions of the studied tissue or lipid, the maximal changes occurred in the percentage of saturated acids (4–83%); the percentage of unsaturated acids was less expressed (1–14%) and the changes in unsaturation index (UI), on average, did not exceed 20%. It was suggested that the revealed quantitative restriction of the UI change under the action of various external factors is a limit for maintenance of the membrane fluidity necessary for normal cell viability, specifically in the studied ectothermic molluscs.