ANATOMY OF SOME INDO-PACIFIC ELYSIIDAE (OPISTHOBRANCHIA: SACOGLOSSA (=ASCOGLOSSA)), WITH A DISCUSSION OF THE GENERIC DIVISION AND PHYLOGENY

The Elysiidae is the largest family of Sacoglossa (=Ascoglossa)(Mollusca, Opisthobranchia). The Indo-Pacific fauna containsabout 65 species presently referred to the genus Elysia. Almostnothing is known about the internal anatomy of these animals.In the present study the internal anatomy, particularly thepharyngeal musculature, morphology of radularteeth, and reproductivesystems, of 12 Indo-Pacific elysiids is investigated. Also,the internal anatomy of the Mediterranean type species of thegenera Elysia and Thuridilla is described. On this basis, thevalidity of the genera Elysia, Thuridilla, Elysiella and Pattyclaya,is confirmed. Also, the genus Placobranchus is transferred tothe Elysiidae. phylogenetically important characters are identifiedand phylogenetic relationships within the family are discussed. (Received 10 April 1991; accepted 28 December 1991)