A, cladogram of the evolution of opistobranch species (adapted from a recent cladistic analysis of mDNA sequence and conventional character traits; Medina & Walsh, 2000). All species except Bulla are in the family Aplysiidae. B-D, pictures of the different species used in the present study: Dolabrifera (B), Phyllaplysia (C) and Aplysia (D). Wild-caught adult Aplysia individuals are usually much larger (about 250 g body weight, 15 cm long) than their Dolabrifera and Phyllaplysia counterparts (2–3 g body weight, 3 cm long).