The gymnosomatous and thecosomatous pteropods, Clione limacina and its only prey Limacina helicina and L. retroversa, from Arctic and Antarctic waters as well as particulate matter have been investigated with respect to their lipid compositions. The close trophic relationships between phytoplankton-Limacina-Clione were partially reflected by the fatty acid compositions due to high mounts of 16:1(n - 7), which indicate the ingestion of diatoms in L. helicina. However, the outstanding feature of this food chain concerns the extraordinary lipid and fatty acid compositions of C. limacina. Up to 40.6% of its total lipid consisted of 1-O-alkyldiacylglycerol ethers, a very unusual depot lipid in the zooplankton. The other major storage lipid were triacylglycerols, which occurred in similar amounts. In addition, the various lipid classes of C. limacina exhibited unique fatty acid compositions, due to high percentages of odd-chain length components, up to one third of total fatty acids. The dominant odd-chain fatty acid was 17:l(n - 8) reaching 18%, followed by 15:0 and 17:0, with 17:l(n - 8) enriched in the diacylglycerol ethers. Major even-chain fatty acids were 16:0, 16:l(n - 7), 20:5(n - 3) and 22:6(n - 3). In L. helicina neither diacylglycerol ethers nor odd-chain fatty acids could be detected, indicating that these atypical lipids are not ingested with the prey by C. limacina. De novo biosynthesis of these compounds is therefore suggested. The synthesis of odd-chain fatty acids is initiated with propionate. This precursor may originate from dimethyl-β-propiothetin (DMPT), which has been described to be accumulated by L. helicina via phytoplankton uptake. Hence, C. limacina not only represents an exceptional member of the polar zooplankton due to its extreme trophic specialisation, it has also developed exceptional lipid biochemical adaptations in the Arctic and Antarctic ocean.