Morphological and molecular data obtained from Hawaiian sea hares identified as Aplysia dactylomela (Rang) and Aplysia pulmonica (Gould) revealed that they belong to the same species. A review of the literature shows that the name A. pulmonica has been used inconsistently, but the specimens we examined match the original description of the species. Two other closely related species, Aplysia kurodai (Baba) and Aplysia oculifera (Adams & Reeve), are distinct. In addition, Caribbean specimens of A. dactylomela are genetically and morphologically distinct from Indo-Pacific A. dactylomela. Because the name A. dactylomela was introduced for Atlantic specimens, it is here proposed that the name Aplysia argus (Ruppell & Leuckart) should be used for Indo-Pacific sea hares previously identified as A. dactylomela.