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In this study, we determined the whole mitochondrial genome profile of the three-spot swimming crab (Portunus sanguinolentus) and elucidated phylogenetic relationships between representative species in the order Decapoda. The mitochondrial genome was 16,024 bp in length and consisted of 13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes, and a putative control region. Of the 37 genes, 23 were encoded by the heavy strand while 14 were encoded by the light strand. Four types of start codons were identified; ATG initiated nine genes, ATT initiated two genes, and ATC and GTG each started one gene. Nine protein-coding genes ended with a complete TAA or TAG stop codon, and four genes ended with an incomplete T or TA codon. Fourteen non-coding regions were found, which ranged from 1 to 34 bp in length. Nine overlaps were observed, with lengths between 1 and 7 bp. Phylogenetic analysis suggested that P. sanguinolentus is genetically closest to P. trituberculatus and P. pelagicus. Charybdis feriata, C. japonica, and Thalamita crenata formed a single cluster, and were close to the genera Callinectes and Portunus. Therefore, the genera Charybdis and Thalamita should be classified into the subfamily Portuninae., Competing Interests: The authors declare no conflict of interest.

This study determined the mitochondrial genome structure of the blue swimming crab (Portunus pelagicus), and elucidated its phylogenetic relationships among the species within the order Decapoda. The complete mitochondrial genome was 16,155 bp long, and contained 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and 1 DNA control region. The gene order of the genome was the same as that found within the family Portunidae. Twenty-three genes were on the heavy strand and 14 were on the light strand. Almost all of the protein-coding genes were initiated by an ATG codon, except for three genes (ATP6, ND1, and ND3) that started with a rare ATT codon. Of the 13 protein-coding genes, 10 ended with complete TAA or TAG stop codons and three ended with an incomplete T codon. Thirteen non-coding regions were identified that ranged from 1 to 30 bp in length. Nine overlaps were found, which ranged 1 to 7 bp in length. Phylogenetic analyses based on 12 concatenated protein-coding genes revealed that P. pelagicus formed a monophyletic group with Portunus trituberculatus, which were in a larger group with Callinectes sapidus, while the genera Charybdis and Thalamita formed another group. These two groups clustered together and grouped with the genus Scylla. The phylogenetic analysis supported the inclusion of Charybdis in subfamily Portuninae of the family Portunidae, and revealed a close relationship between Charybdis and Thalamita. We suggest that Thalamita should also be classified into the subfamily Portuninae. The results can be used in the study of phylogenetic, population genetic and conservation genetics of P. pelagicus., Competing Interests: The authors declare no conflict of interest.