A description of two new deep-sea nemerteans from North Pacific with reconsideration of the genus Oerstedia (Hoplonemertea, Oerstediidae)

To date, a total of 30 nemertean species have been described from depths greater than 1000 m. All deep-sea species of the infraorder Oerstediina belong to the genera found at great depths only. A new species of the genus Oerstedia Quatrefages, 1846 (O. sashae sp. nov.), whose described species inhabit shallow waters, has been collected on the Emperor Seamounts from a depth of 1407 m. Oerstedia sashae sp. nov. differs from the other species of the genus by the lack of eyes. Another new species, Oerstedia sofiae sp. nov., which is very close to the symbiotic Cryptonemertes actinophila (Bürger, 1904), has been described from the Sea of Okhotsk, from a depth of 250–490 m. A phylogenetic analysis based on five gene markers (COI, 16 S, 18 S, 28 S, and histone H3) has shown that O. sashae sp. nov., O. sofiae sp. nov., and C. actinophila belong to clade Paroerstediella of the genus Oerstedia. Cryptonemertes actinophila is here proposed to be transferred to the genus Oerstedia. Oerstedia sofiae sp. nov. and O. actinophila comb. nov. differ from the other species of the genus by the red blood and a very short proboscis and rhynchocoel. •Eyeless Oerstedia sashae sp. nov. is described from bathyal of the Emperor Seamounts.•Symbiotic Oerstedia sofiae sp. nov. is described from bathyal of the Sea of Okhotsk.•Genus Cryptonemertes is a junior synonym of the Oerstedia.