Phylogenetic Relationships of Japanese Unionoida (Mollusca: Bivalvia) Based on Mitochondrial 16S rDNA Sequences

Japanese unionoid mussels are classified into 2 families (Margaritiferidae and Unionidae), 12 genera, and 18 species based on the morphological characteristics of both adults and larvae; however, there are some debates regarding their systematics. In this study, we determined mitochondrial 16S ribosomal DNA sequences (347-bp) for 60 specimens belonging to 18 species and constructed trees to elucidate phylogenetic relationships and evaluate the current systematics of Japanese unionoid mussels. Almost all species formed clades, except for Inversiunio yanagawensis, Sinanodonta lauta, S. japonica, and Margaritifera laevis, even though two or more specimens were collected from distant localities. All genera formed highly supported clades with the exception of the genus Sinanodonta. Phylogenetic relationships obtained in this study supported systematics based on morphological and larval traits. Therefore, the current phylogenetic relationships and systematics of Japanese unionoid mussels are stronger than they were before; now that they are corroborated by genetic data.