RIBOSOMAL-RNA PHYLOGENY OF SELECTED MAJOR CLADES IN THE MOLLUSCA

New sequence data from the D6 region of 28S rRNA and rDNA are presente d for 28 species of molluscs and two annelids. These sequences were an alyzed along with previously published molluscan sequences. Five of th e molluscan classes were represented: Gastropoda, Cephalopoda, Bivalvi a, Scaphopoda, and Polyplacophora, the last two by only one species ea ch. Allowing for presumed long branch effects of Helicinidae, Patellid ae, and the annelids, cladistic analysis supported monophyly of the fo llowing groups: Cephalopoda, Nautiloida, Coleoida, Gastropoda, Apogast ropoda, Caenogastropoda, Neogastropoda, Rissooidea, Pulmonata, Stylomm atophora, and a subset of Heterodonta including Sphaeriidae, Dreisseni dae, and Veneridae but not Cardiidae. No resolution of relationships a mong molluscan classes was obtained.