New clades of euthyneuran gastropods (Mollusca) from 28S rRNA sequences

Recent morphological and molecular results on phylogeny of euthyneuran gast ropods, which include opisthobranchs and pulmonates, have greatly diminishe d previous supposed resolution of their phylogenetic relationships. In addi tion to recent morphological results, sequences of the D1 and D2 domains of the 28S rRNA are here analyzed by parsimony for 31 euthyneuran species. Th e molecular and previous morphological data sets were not congruent accordi ng to an ILD test, and morphological and molecular data could not be analyz ed simultaneously. Consequently Bremer's Combinable Component Consensus was used to obtain a new tree, with the following supported molecular results: monophyly of a new clade of opisthobranchs including actively swimming Eut hyneura, i.e,, pelagic Gymnosomata and Thecosomata plus benthic Anaspidea; fist molecular confirmation of monophylies of Hygrophila, including Chilina , Acteonoidea, and Sacoglossa, which include both shell-bearing species and slugs; and new confirmation of the monophyly of Stylommatophora, Morpholog ical characters which support the new clades obtained here are discussed. ( C) 2001 Academic Press.