A recent molecular study on pelagic nudibranchs showed that Glaucus marginatus (Reinhardt and Bergh, 1864) is a complex of three cryptic species, whereas the congener G. atlanticus (Forster, 1777) remain as one species. The objective of the present study was to determine the identity of pelagic nudibranchs collected in the Gulf of California using both molecular and traditional taxonomy. New DNA sequences (COI) and GenBank data were used to confirm the specimens' identity as G. atlanticus. Records from G. atlanticus were obtained from databases to determine the species geographic range. Present results increase that range northwards by approximately 150 km in the Gulf of California. Molecular data indicate that G. atlanticus from the Gulf has a wide infl uence from populations from the North and South Pacific and Indian Oceans. There is no current evidence of other cryptic species.