The Complete Mitochondrial Genome of Portunion sinensis (Crustacea: Isopoda) and Its Phylogenies

In this study, we conducted molecular identification and complete mitochondrial genome annotation of isopod parasites isolated from mud crabs (<i>Scylla paramamosain</i>) in the China Sea. The specimen was identified as <i>Portunion sinensis</i>, a recently described species of the family Entoniscidae. <i>P. sinensis</i> is characterized by an anterior thorax positioned vertically and posterior ventral processes directed backwards; the female's marsupium is formed by the close adhesion of oostegites to the host membrane; the first oostegite is differentiated into three parts; the pleopoda have well-developed lamellar and pleural lamellae; and two ventral ovarian processes are present along with a pair of dorsal processes. The complete mitochondrial genome of the parasite is 14,603 bp in length, containing 35 genes (13 protein-coding genes, 20 transfer RNAs, and 2 ribosomal RNAs) as well as a putative control region (CR) located between the <i>cob</i> and <i>nad1</i> genes. This study represents the initial characterization of the mitochondrial genome of <i>P. sinensis</i>. These findings provide molecular validation of its status as an independent species and lay the groundwork for the future identification of parasites within the genus <i>Portunion</i>. These data provide a necessary molecular reference for future research into the systematics and evolutionary history of decapod-infesting parasites.