Molecular phylogeny of venus clams (Mollusca, Bivalvia, Veneridae) with emphasis on the systematic position of taxa along the coast of mainland China

Veneridae is the most richly speciose family of heterodont bivalves with high ecological and economic value. Attention to the Veneridae systematics has been raised since traditional conchology-based ideas on relationships among the venerids were challenged by recent studies using molecular makers and other new approaches and methods. Herein, DNA sequence information from fragments of two mitochondrial genes (COI and 16S) and one nuclear protein-coding gene (H3) for 135 taxa (128 venerids, five nonvenerid veneroids and two other outgroups) are used to reconstruct the phylogenetic relationships of venus clams under maximum parsimony, maximum likelihood and Bayesian inference approaches. According to our molecular results, the traditional Veneridae is not recovered as monophyletic and most of the nominal subfamilies and genera formed para-polyphyletic clades. The findings indicate that the current venerid classification cannot validly reflect a natural subdivision. In the present study, the classification of taxa along the coast of mainland China within this family are also revised based on their phylogenetic position and morphological characters. The synonymization of chionine genus Placamen with Clausinella is rejected. Chionine subgenera Anomalodiscus and Cryptonema are given full generic rank again and incorporated into Venerinae and Tapetinae, respectively. Tapetine Marcia hiantina, M. japonica and M. marmorata were distantly related to Katelysia spp., so assigning those three species into the genus Katelysia by some malacologists is rejected herein. Our results also evidence that the synonymization of the genus Tigammona and Periglypta might be inappropriate.