A molecular phylogeny of North American Pleuroceridae (Gastropoda : Cerithioidea) based on mitochondrial 16S rDNA sequences

The Pleuroceridae Fischer, 1885, is one of three freshwater gastropod famil ies currently recognized in the superfamily Cerithioidea Ferussac, 1819 (Mo llusca: Caenogastropoda Cox, 1960). Despite considerable literature justify ing various proposed generic names of North American pleurocerids, no study has been conducted examining phylogenetic relationships of the recognized genera. In an effort to expand our understanding of evolutionary relationsh ips of North American pleurocerid genrea, we examined a large portion of th e mitochondrial 16S rRNA gene among 32 extant North American taxa. Multiple sequence alignment of the amplified region for our taxa resulted in a matr ix consisting of 900 nucleotides including insertions and deletions. Based on analysis of nucleotide substitution patterns, we employed two approaches in our phylogenetic analysis: (1) all substitutions received equal weighti ng and (2) transversions were weighted 2X and 4X transitions to compensate for transition saturation among distantly related taxa. The molecular phylo geny based on the mitochondrial 16S rDNA sequences supports the monophyly o f Pleurocera Rafinesque, 1819, Elimia H.&A. Adams, 1854, and Juga H.&A. Ada ms, 1854, but depicts the genera Lithasia Haldeman, 1840, and Leptoxis Rafi nesque, 1819, as polyphyletic. The genus Pleurocera is sister to Elimia, wh ich in turn is sister to a paraphyletic assemblage including representative s of Leptoxis, Lithasia, and the monotypic genus 10 Lea, 1831. Juga, a genu s restricted to west of the North American continental divide is the basal- most clads and is sister to all the aforementioned genera found east of the continental divide.