With an estimated 8,000-20,000 species, bivalves represent the second largest living class of molluscs (Bieler et al. 2013). Revived interest in molluscan phylogeny has resulted in a torrent of molecular sequence data from phylogenetic, mitogenomic, and phylogenomic studies. Despite recent progress, basal relationships of the class Bivalvia remain contentious, owing to conflicting hypotheses often between morphology and molecules.
