Phylogenetic relationships among five sea-hare species (order Anaspidea) were inferred from analyses of orthologous amino acid sequences of monomeric myoglobins. The genus Aplysia is shown to be monophyletic, but the data do not support the clustering of A. kurodai and A. limacina into the subgenus Varria to the exclusion of A. juliana. Rather, A. juliana and A. kurodai are shown to be phylogenetically closer to each other than either is to A. limacina. The inferred molecular phylogenetic arrangements support neither the assignment of Dolabella to a distinct anaspid family nor the separation of Bursatella from Aplysia and Dolabella.