The complete mitochondrial genome of Calappa bilineata: The first representative from the family Calappidae and its phylogenetic position within Brachyura.

In this study, we determined the complete mitogenome sequence of Calappa bilineata, which is the first mitogenome of Calappidae up to now. The total length is 15,606 bp and includes 13 protein-coding genes, 22 transfer RNAs, two ribosomal RNAs and one control region. The genome composition is highly A + T biased (68.7%), and exhibits a negative AT-skew (-0.010) and GC-skew (-0.267). As with other invertebrate mitogenomes, the PCGs start with the standard ATN and stop with the standard TAN codons or incomplete T. Phylogenetic analysis showed that C. bilineata was most closely related to Matuta planipes (Matutidae), and these two species formed a sister clade, constituting a Calappoidea group and forming a sister clade with part of Eriphioidea. The existence of the polyphyletic families raised doubts over the traditional classification system. These results will help to better understand the features of the C. bilineata mitogenome and lay foundation for further evolutionary relationships within Brachyura.