Nemerteans collected in the Bering Sea during the research cruises aboard the R/V Akademik M.A. Lavrentyev in 2016, 2018, and 2021 with an analysis of deep-sea heteronemertean and hoplonemertean species

During the research cruises aboard the R/V Akademik M.A. Lavrentyev in 2016, 2018, and 2021 four nemertean species were collected from the bathyal zone of the Bering Sea: Cerebratulus mordukhovichi sp. nov., Lineidae sp. Bering G06, Nipponnemertes cf. rubella (Koryak slope, depths 420–662 m), and Oerstedia sp. (Piip Volcano, depth 783–984 m). These species, as well as deep-sea nemerteans collected in the Northwestern Pacific, the North Atlantic, Arctic, and Antarctic, were included in a phylogenetic analysis of Lineidae, Cratenemertidae, and Oerstediidae based on five gene markers (COI, 16S, 18S, 28S, and histone H3). It has been shown that deep-sea species of Lineidae are found in 8 phylogenetic lineages out of 12, with new Lineage Q comprised only of deep-sea species. Lineidae sp. Bering G06 belongs to Lineage G and is closely related to Lineidae sp. 3DS from the abyssal zone of the Sea of Okhotsk. Cerebratulus mordukhovichi sp. nov., found in the Bering Sea and off the Kuril Islands, belongs to Lineage J and the subclade including “Micrura” bathyalis, Cerebratulus herculeus, and Cerebratulus californiensis. Nipponnemertes cf. rubella, found at depths from 5 to 662 m in the Bering Sea, off the Kuril Islands, and California, belongs to clade A and is very close to N. pulchra (with COI p-distances within 3.8–4.3%). Oerstedia sp. is the deepest-dwelling of all known members of the genus Oerstedia, but it does not belong to any of the two clades (Oerstedia and Paroerstediella) of this genus. The subgenus Kurilonemertes Chernyshev, 1993 is upgraded to the genus level. The assumption on eurybathic distribution of any nemertean species should be supported by genetic methods. Pseudomicrura afzelii and Gononemertes parasita are confirmed to be eurybathic species found at depths from 15–70 m–886 m. •Deep-sea lineids are found in 8 lineages, with one lineage comprised only of deep-sea species.•All individuals identified as Oerstedia form a single highly supported clade.•The subgenus Kurilonemertes Chernyshev, 1993 is upgraded to the genus level.