The FA composition of the pelagic jellyfish Aurelia sp. collected from off-shore Western Australia waters was determined by capillary GC and GC-MS, with confirmation of PUFA structure performed by analysis of 4,4-dimethyloxazoline derivatives. PUFA constituted 47.6% of the total FA, with the essential PUFA eicosapentaenoic acid (EPA), arachidonic acid, and DHA accounting for 34%. Of particular interest, the unusual very long chain PUFA 6,9,12,15,18,21-tetracosahexaenoic acid (THA, 24:6n-3) was present at 9.3%, and the rarely reported 6,9,12,15,18-tetracosapentaenoic acid (24:5n-6) also was detected at 0.8%. To our knowledge, this represents the first report of THA as a major PUFA in a pelagic marine organism.