The complete mitochondrial genome of the black mud crab, Scylla serrata (Crustacea: Brachyura: Portunidae) and its phylogenetic position among (pan)crustaceans.

The black mud crab, Scylla serrata (Forskål 1775), is the most economically important edible crab in South-East Asia. In the present study, the complete mitochondrial genome of black mud crab, S. serrata, was determined with the sequential polymerase chain reaction and primer walking sequencing. The complete mitochondrial genome was 15,721 bp in length with an A+T content of 69.2 % and contained 37 mitochondrial genes (13 protein coding genes (PCGs), 2 ribosomal RNA genes and 22 transfer RNA genes) and a control region (CR). The analysis of the CR sequence shows that it contains a multitude of repetitive fragments which can fold into hairpin-like or secondary structures and conserved elements as in other arthropods. The gene order of S. serrata mainly retains as the pancrustacean ground pattern, except for a single translocation of trnH. The gene arrangement of S. serrata appears to be a typical feature of portunid crabs. Phylogenetic analyses with concatenated amino acid sequences of 12 PCGs establishes that S. serrata in a well-supported monophyletic Portunidae and is consistent with previous morphological classification. Moreover, the phylogenomic results strongly support monophyletic Pancrustacea (Hexapoda plus "Crustaceans"). Within Pancrustacea, this study identifies Malacostraca + Entomostraca and Branchiopoda as the sister group to Hexapoda, which confirms that "Crustacea" is not monophyletic. Cirripedia + Remipedia appear to be a basal lineage of Pancrustacea. The present study also provides considerable data for the application of both population and phylogenetic studies of other crab species.