A phylogenetic assessment of <i>Pronoprymna</i> spp. (Digenea: Faustulidae) and Pacific and Antarctic representatives of the genus <i>Steringophorus</i> Odhner, 1905 (Digenea: Fellodistomidae), with description of a new species

In this study, we elucidated the phylogenetic position of a Pacific species <i>Pronoprymna petrowi</i>, a Caspian species <i>Pronoprymna ventricosa</i>, an Antarctic species of the genus <i>Steringophorus, S. liparidis</i>, and a new species of the same genus, <i>S. occidentalipacificus</i> sp. nov. The new species was found in a bathylagid fish <i>Leuroglossus schmidti</i> from the Sea of Okhotsk. <i>Steringophorus occidentalipacificus</i> sp. nov. is similar to <i>S. congeri</i>, and differs from it in the length of the body and the forebody, the shape of the testes, the sucker-ratio, the size of eggs and the extension of the caeca and the cirrus-sac. The <i>28S rRNA</i> gene-based analyses supported a sister relationship between <i>Pr. petrowi</i> and <i>Pr. ventricosa</i>, and put the genus <i>Pronoprymna</i> into to the group of faustulids (<i>sensu lato</i>), which is nested within the Gymnophaloidea clade. Based on the results of these analyses, <i>Steringophorus</i> is identified as a paraphyletic taxon within the Fellodistomidae (Gymnophalloidea). Phylogenic reconstructions also support a morphologically identified sister relationship between S. <i>liparidis</i> and <i>S. thulini</i> and demonstrate a close relationship of <i>S. occidentalipacificus</i> sp. nov. with <i>S. blackeri</i> and <i>S. pritchardae</i>. The analysis of the <i>nd1</i> gene sequences also confirmed the phylogenetic affinity of S. <i>liparidis</i> to <i>S. thulini</i>. urn:lsid:zoobank.org:pub:6217E5D2-00FD-4135-A8DA-CDBAFACA52