Molecular phylogeny of Acanthochitonina (Mollusca: Polyplacophora: Chitonida): three new mitochondrial genomes, rearranged gene orders and systematics

Few molecular studies have addressed the phylogenetic relationships within Acanthochitonina. Here, we use high-throughput sequencing to determine three mitochondrial genomes of Acanthochitonina. We further explore phylogenetic relationships with expanded taxon sampling based on mitochondrial and nuclear sequence data. Phylogenetic analyses recover two major lineages roughly corresponding to Cryptoplacoidea and Mopalioidea, but the necessity of reassigning multiple genera challenges their conventional definition and that of the families Mopaliidae, Schizoplacidae and Lepidochitonidae. Two mitogenomes share a gene rearrangement that might represent a synapomorphy for Lepidochitonidae. Our phylogenetic results support the reinterpretation of certain morphological characters as homologous, previously assumed to be convergent. They further reveal that major Acanthochitonina lineages were restricted to particular ocean basins, where they diverged into endemisms with disparate morphology. Our results are corroborated by morphological and biogeographical evidence and contribute toward resolving the phylogenetic relationships of Acanthochitonina, and highlight the need for further phylogenetic and systematic studies.