Two complete mitogenomes of Ocypodoidea (Decapoda: Brachyura), Cleistostoma dilatatum (Camptandriidae) and Euplax sp. (Macrophthalmidae) and its phylogenetic implications

Complete mitochondrial genomes (mitogenomes) can provide useful information for phylogenetic relationships, gene rearrangement, and molecular evolution. In the present study, two newly sequenced mitogenomes of Ocypodoidea (Cleistostoma dilatatum and Euplax sp.) were reported for the first time, which are 15 444 bp and 16 129 bp in length, respectively. Cleistostoma dilatatum is the first species in the family Camptandriidae whose complete mitogenome was sequenced. Each mitogenome contains an entire set of 37 genes and a putative control region, but their gene arrangements are largely different. Tandem duplication and random loss model is proposed to account for their gene arrangements. Comparative genomic analyses of 19 mitogenomes clustering in one branch reveal that 18 of them shared the same gene rearrangement, while that of C. dilatatum mitogenome was consistent with the ancestral gene arrangement of Brachyura. The dN/dS ratio analysis shows that all PCGs are evolving under purifying selection. Phylogenetic analyses show that all Macrophalmidae species cluster together as a group, and then form a sister clade with Camptandriidae. Moreover, the polyphyly of three superfamilies (Ocypodoidea, Eriphioidea, and Grapsoidea) is reconfirmed. These findings help to confirm the phylogenetic position of Camptandriidae, as well as provide new insights into the phylogeny of Brachyura.