Complete mitochondrial genome of Echinorhynchus gadi (Acanthocephala, Echinorhynchida) and its phylogenetic implications

The Echinorhynchidae has a long research history, but its mitochondrial genome evolution remains poorly understood, hindering phylogenetic resolution. In this study, we report the first complete mitochondrial genome of the genus <i>Echinorhynchus</i>, obtained from its type species, <i>Echinorhynchus gadi</i>. The circular mitogenome was 17,696 bp in length and contained 39 genes: 12 protein-coding genes (lacking <i>atp8</i>), two ribosomal RNA genes, and 25 transfer RNA genes, including two extra copies of <i>trnW</i> and one extra copy of <i>trnV</i>. Five non-coding regions were identified; the major non-coding region contained tandem repeats and pseudogene fragments, consistent with a tandem duplication and random loss mechanism. Phylogenetic analysis based on the concatenated amino acid sequences of the 12 protein-coding genes placed <i>E. gadi</i> and <i>E. truttae</i> in a well-supported monophyletic clade representing the genus <i>Echinorhynchus</i>. This clade was sister to <i>Aspersentis megarhynchus</i>, supporting a close relationship between Echinorhynchidae and Heteracanthocephalidae. Because the published <i>E. truttae</i> mitogenome is incomplete, this study fills a critical genomic gap and provides a valuable molecular resource for future taxonomic, systematic, and evolutionary studies of Acanthocephala.