Qualitative and quantitative distribution of ether phospholipids was studied in several aquatic organisms. 2. Brain, nerve and gills of these animals were rich in ether glycerophospholipids. 3. 1-alkenyl ethers were in general more abundant than alkyl ones. The alkenyl ethers were mainly components of PE in all aquatic animals. Those of PS occurred in mollusca only. 4. Alkyl ether moieties appeared to be essentially located in PE and PC. 5. This review suggests that ether phospholipids may play an important role in the permeability properties of biological membranes.