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