The phospholipid fatty acids from the sponge Cribrochalina vasculum were studied, revealing the presence of the new 23-methyl-5,9-pentacosadienoic acid (26:2) which completes the iso-anteiso 26:2 (delta 5,9) series. Other phospholipid fatty acids isolated include 26-methyl-5,9-heptacosadienoic (28:2) and 25-methyl-5,9-heptacosadienoic (28:2), as well as the branched acids 8-methylhexadecanoic and 11-methyloctadecanoic. The fatty acids described in this work were found in phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol. The sterol composition of C. vasculum consisted of petrosterol, an interesting cyclopropane containing sterol, and the more common sitosterol. The phospholipid fatty acid composition of the demosponge Ircinia strobilina is also reported upon.