Towards a molecular phylogeny of Mollusks: Bivalves' early evolution as revealed by mitochondrial genes

► Four mitochondrial genes (12s, 16s, cox1, cytb) were sequenced in 28 species of bivalve mollusks. ► A phylogenetic analysis was carried out on 1909 sites from a total of 55 bivalve taxa and 4 outgroups. ► The codon-based Bayesian analysis yielded most reliable tree, on which split dates were computed. ► Most subclasses resulted monophyletic: Palaeoheterodonta, Pteriomorphia, Heterodonta. ► Nuculanoidea and Anomalodesmata respectively nest within and basal to pteriomorphians.