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

Recent morphological and molecular results on phylogeny of euthyneuran gastropods, which include opisthobranchs and pulmonates, have greatly diminished previous supposed resolution of their phylogenetic relationships. In addition to recent morphological results, sequences of the D1 and D2 domains of the 28S rRNA are here analyzed by parsimony for 31 euthyneuran species. The molecular and previous morphological data sets were not congruent according to an ILD test, and morphological and molecular data could not be analyzed 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 Euthyneura, i.e., pelagic Gymnosomata and Thecosomata plus benthic Anaspidea; first 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. Morphological characters which support the new clades obtained here are discussed. Copyright 2001 Academic Press.