Phylogeny of two accacoeliid species (Digenea: Hemiuroidea) ex <i>Mola mola</i> (Linnaeus, 1758) (Tetraodontiformes: Molidae) from Northwest Pacific, with first molecular data on <i>Odhnerium</i> Yamaguti, 1934

Accacoeliid digeneans associated with fish of the family Molidae exhibit enigmatically high taxonomic diversity. However, the phylogenetic relationships between species within this digenean taxon are poorly understood. In the present study, the first nuclear <i>28S rRNA</i> gene, ITS2 region of nuclear DNA, and mitochondrial <i>cox1</i> gene sequence datasets were obtained for two members of the Accacoeliidae, a type and only species of the genus <i>Odhnerium</i> Yamaguti 1934 and an unidentified <i>Accacladocoelium</i> sp. collected from <i>Mola mola</i> (Linnaeus, 1758) off Iturup Island. Analyses of molecular differentiation and phylogenetic relationships indicate that <i>Accacladocoelium</i> sp. is a sister species to <i>Accacladocoelium nigroflavum</i> (Rudolphi, 1819). The genus <i>Odhnerium</i> is closely related to <i>Tetrochetus</i> Looss, 1912, on the <i>28S rRNA</i> gene-based phylogenetic tree. Results of phylogenetic analysis based on both the mitochondrial <i>cox1</i> gene and the concatenated ribosomal ITS2 region and <i>cox1</i> gene of mtDNA show that the genus <i>Odhnerium</i> is close to the <i>A. nigroflavum</i> + <i>Accacladocoelium</i> sp. clade. In turn, the genus <i>Accacladocoelium</i> does not have monophyletic status in the trees reconstructed from these data.