(Opisthobranchia: Cephalaspidea), Haminoea callidegenita
, is described from Washington State, U.S.A. Diagnostic features are reddish brown colour, deeply bifurcate cephalic shield, reddish ovate shell with imperforate apex, tubular Hancock's organ, unarmed penis, unilobular prostate, and radula formula n.l.l.l.n (n from 12 to 21), with bicuspid first lateral uncini. The development of H. callidegenita
is unusual among the Opisthobranchia in that the hatching stage includes both lecithotrophic veligers and juveniles from each egg mass. Diagnostic features were examined among animals from different populations of H. callidegenita
and two other Haminoea
species found in the northeast Pacific: H. vesicula
Gould, 1855 and H. virescens
Sowerby, 1833. Shell shape was slightly variable among individuals of all three species and radula morphologies were variable among populations of H. vesicula
. Fingerlike papillae were noted on the gizzard plates and are suggested as a diagnostic character.