Phylogenetic relationships among four superfamilies in Tanaidacea (Peracarida) inferred from mitochondrial genomes

Abstract Tanaidacea contains about 1600 species across four superfamilies (Apseudoidea, Neotanaoidea, Paratanaoidea, and Tanaidoidea). Phylogenetic relationships among the four superfamilies had been investigated molecularly with one to several genes, or with transcriptome data, but not with mitochondrial genome (mitogenome) data. Mitogenome data were available only for Pseudotanais sp. (Paratanaoidea) and Arctotanais alascensis (Tanaidoidea). We sequenced and annotated a complete mitogenome sequence for Sinelobus kisui (Tanaidoidea) and nearly complete mitogenome sequences for Apseudes nipponicus , Apseudes ranma , Carpoapseudes spinigena (Apseudoidea), and Neotanais sp. (Neotanaoidea). We detected the typical two rRNA and 13 protein-coding genes (PCGs) in all five species, but failed to detect one to five tRNAs in each species. The gene orders of the four superfamilies differed from the pancrustacean ground pattern and from one another. In maximum-likelihood phylogenetic trees based on amino acid and nucleotide datasets for the 13 PCGs and two rRNA genes, Tanaidacea emerged as a weakly supported sister clade to Isopoda. Within Tanaidacea, a fully supported Apseudoidea was the sister group to a moderately supported clade comprising the other three superfamilies; in the latter clade, a weakly supported Tanaidoidea clade was successively sister to Paratanaoidea and then to Neotanaoidea. The mitogenome-based topology among the four superfamilies differed from previous topologies based on 18S rRNA or transcriptome data (Apseudoidea, (Paratanaoidea, (Neotanaoidea, Tanaidoidea))). This contradiction suggests possible effects of mito–nuclear discordance or long-branch attraction for Pseudotanais sp. and S. kisui .