Trans-Arctic distribution of marine fish digenean Progonus muelleri (Derogenidae) tested by molecular data

In the digenean superfamily Hemiuroidea, a number of species are registered from a wide geographic range including the Arctic, Atlantic and Pacific Oceans. However, these distributions have not yet been confirmed with the molecular methods. In the present study, we performed molecular analysis of Progonus muelleri (Levinsen, 1881) (Derogenidae) from distant regions: the European sub-Arctic (the White, Barents and Pechora Seas) and the Pacific Northwest (the Sea of Okhotsk and the Pacific coast of the northern Kuril Islands). Two genetic lineages within P. muelleri, PM1 and PM2, are proved to occur in sympatry in the European sub-Arctic. We found minor differences in their maritae structure, and thus suppose they represent two pseudocryptic species. PM1 was also registered in the Pacific Northwest (PM1b) where it has differences in cox1 gene from the European sub-Arctic lineage (PM1a). The intramolluscan life-cycle stages of P. muelleri from the Sea of Okhotsk are described and compared with the ones from the White Sea. We hypothesize that PM1a, PM1b and PM2 are three distinct species, but this should be further tested.