Abstract

Simple SummaryThe mud crab (Scylla paramamosain) is an economically important crustacean species. This study reports the first complete mitochondrial genome of the parasitic isopodPortunion sinensis(family Entoniscidae) infecting this crab. We conducted a detailed analysis of its genomic architecture, revealing a compact genome and unique structural characteristics. As the first representative mitochondrial genome for the family Entoniscidae, this work fills a critical gap in molecular data for the superfamily Bopyroidea. These findings not only provide essential genetic resources for species identification but also serve as a key reference for elucidating the mitochondrial structure and phylogenetic relationships of parasitic crustaceans.In this study, we conducted molecular identification and complete mitochondrial genome annotation of isopod parasites isolated from mud crabs (Scylla paramamosain) in the China Sea. The specimen was identified asPortunion sinensis, a recently described species of the family Entoniscidae.P. sinensisis 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 thecobandnad1genes. This study represents the initial characterization of the mitochondrial genome ofP. sinensis. These findings provide molecular validation of its status as an independent species and lay the groundwork for