Delimiting the polymorphic congeners of the genus Oerstedia Quatrefages, 1864 (Nemertea, Hoplonemertea), and descriptions of three new species from the Northwest Pacific

Three new species of the monostiliferous hoplonemertean genus Oerstedia Quatrefages, 1864, are herein described using morphological and molecular data—Oerstedia pseudoculata sp. nov., from Akkeshi Bay and Oshoro Bay, Hokkaido, Japan, and from Aniwa Bay, Sakhalin, Russia; Oerstedia rugosa sp. nov. from Sagami Bay, Misaki, Kanagawa, Japan, and Van Phong Bay, Vietnam; and Oerstedia viridifusca sp. nov. from Manazuru, Kanagawa, Japan. As to the external morphology, O. pseudoculata sp. nov. can be differentiated from O. oculata only by its bright-orange ocelli visible on both sides of the head, and a proboscis pore opening at the ventral tip of the head. These two sister species repeat each other’s color patterns, a phenomenon that can be explained by Vavilov’s law of homologous series. Oerstedia rugosa sp. nov. can be identified by its carmine or deep-red to brownish-red body with several longitudinal, intertwined white lines or wrinkles running from the head to the posterior body, and by 17–23 vaguely bordered white bands composed of variedly sized dots encircling the body, arranged at irregular intervals. Oerstedia viridifusca sp. nov. can be distinguished from other Oerstedia by (i) the entire body flecked with minute greenish-brown dots, especially densely on the anterior portion of the dorsal surface, but sparsely on the posterior half of the ventral surface; (ii) a collar-like portion encircling the body along the posterior cephalic furrow where the greenish-brown dots are absent; (iii) the anterolateral edges of the head lacking the greenish-brown dots; and (iv) the ocelli being brownish-orange in color. Oerstedia phoresiae (Kulikova, 1987) is reported for the first time from Japan, in addition to its previous distribution record in Russia and in South Korea. Phylogenetic analyses based on the 16S, 18S, 28S ribosomal RNA, cytochrome c oxidase subunit I, and histone H3 genes show that the new species are true congeners of the genus Oerstedia with O. pseudoculata sp. nov. and O. viridifusca sp. nov. nested within the clade Paroerstediella whereas O. rugosa sp. nov. in the clade Oerstedia. This taxonomic work emphasizes the importance of DNA barcode sequence in the taxonomy and systematics of the polymorphic congeners of the genus Oerstedia

Molecular Phylogeny of the Genus Nipponnemertes (Nemertea: Monostilifera: Cratenemertidae) and Descriptions of 10 New Species, With Notes on Small Body Size in a Newly Discovered Clade

Nemerteans, or ribbon worms, have been reported from intertidal to hadal depths, often showing bathymetrically wide distribution in genus levels. Although current nemertean systematics practices require to provide DNA sequences and infer phylogenetic relationships with suitable molecular markers, previous molecular systematics on nemerteans are mostly biased toward shallow-water species. Members in the genus Nipponnemertes occur worldwide, from tropical to polar waters and intertidal to bathyal waters. Molecular phylogenetic studies are scarce for the genus; only six shallow-water species of 18 species in the genus were subject to molecular phylogeny. Thus, Nipponnemertes is one candidate that needs to be assessed by genetic approaches. In this study, we performed molecular phylogenetic analyses using 59 specimens in 23 species based on partial sequences of two mitochondrial (16S rRNA and cytochrome c oxidase subunit I) and three nuclear gene markers (18S rRNA, 28S rRNA, and histone H3). Our extensive sampling from intertidal to bathyal waters in the Northwest Pacific significantly updated the fauna of Nipponnemertes in this region from four to 17 species. We herein establish 10 new species and provide an updated species list concisely summarizing all the congeners known from the world. Our phylogenetic tree indicated three major lineages within the genus (herein referred to as “Clade A, B, and C”), each presumably characterized by the combination of morphological characters in the head region. Members in Clade A are: Nipponnemertes pulchra (Johnston, 1837), Nipponnemertes ogumai (Yamaoka, 1947), and several unidentified congeners, characterized by having demarcated head without cephalic patches; members in Clade B are: Nipponnemertes crypta sp. nov., Nipponnemertes jambio sp. nov., Nipponnemertes neonilae sp. nov., and Nipponnemertes ojimaorum sp. nov., species having demarcated head with cephalic patches; members in Clade C are: Nipponnemertes ganahai sp. nov., Nipponnemertes kozaensis sp. nov., Nipponnemertes lactea sp. nov., Nipponnemertes notoensis sp. nov., Nipponnemertes ornata sp. nov., Nipponnemertes sugashimaensis sp. nov., and two unidentified forms collected off Jogashima (Japan) and Guam (USA), species with non-demarcated head lacking cephalic patches. Furthermore, we discuss the evolution of remarkably small body size retained among Clade C

New record of the monostiliferous hoplonemertean Gurjanovella littoralis Uschakov, 1926 from Japan (Nemertea, Hoplonemertea, Monostilifera)

A single specimen of a monostiliferous hoplonemertean, collected from a depth of 25 m in Akkeshi Bay, northern Japan, represents the first record of Gurjanovella littoralis Uschakov, 1926 from the Northwest Pacific. The species has been known only from the type locality, White Sea, Russia, although some planktonic larvae from Oregon, USA, and a juvenile from the Sea of Okhotsk have been identified as a member of the genus by molecular sequence data. Our specimen differs from a topotype from the White Sea by 2.9% of uncorrected p-distance and 3.0% of K2P in terms of partial 658-bp sequence of the mitochondrial cytochrome c oxidase subunit I (COI) gene. Our COI phylogenetic tree indicates that each of the larvae from Oregon and the Sea of Okhotsk belongs in Gurjanovella but represents a different species from G. littoralis

New record of the monostiliferous hoplonemertean Gurjanovella littoralis Uschakov, 1926 from Japan (Nemertea, Hoplonemertea, Monostilifera)

A single specimen of a monostiliferous hoplonemertean, collected from a depth of 25 m in Akkeshi Bay, northern Japan, represents the first record of Gurjanovella littoralis Uschakov, 1926 from the Northwest Pacific. The species has been known only from the type locality, White Sea, Russia, although some planktonic larvae from Oregon, USA, and a juvenile from the Sea of Okhotsk have been identified as a member of the genus by molecular sequence data. Our specimen differs from a topotype from the White Sea by 2.9% of uncorrected p-distance and 3.0% of K2P in terms of partial 658-bp sequence of the mitochondrial cytochrome c oxidase subunit I (COI) gene. Our COI phylogenetic tree indicates that each of the larvae from Oregon and the Sea of Okhotsk belongs in Gurjanovella but represents a different species from G. littoralis

Video S1. Field observation of<i> Potamostoma shizunaiense</i>, filmed by Hikaru Nagano.

Supplementary video for Hookabe et al. (2024) "Osmotic responses and oceanic dispersal of upper brackish nemertean: ecophysiology from field to in-vitro observation"</p

Molecular identity of the Antarctic heteronemertean Parborlasia corrugata (Nemertea : Pilidiophora) from Lützow-Holm Bay

The Antarctic heteronemertean Parborlasia corrugata (McIntosh, 1876) (originally Lineus corrugatus) shows a circumpolar distribution in the Southern Ocean, putatively with high dispersal capacity of the planktonic larva. From the eastern coast of Lutzow-Holm Bay near Syowa Station (69 degrees 00'S, 39 degrees 35'E), several records of heteronemerteans have been made under the name of Lineus corrugatus. However, they have never been explicitly identified by molecular data. In the present study, we determined a partial sequence of the mitochondrial cytochrome c oxidase subunit I (COI) gene for 11 specimens of P. corrugata collected from depths of 17-27 m under sea ice near Syowa Station. A haplotype-network analysis along with other COI sequences from 66 individuals collected at different places in the Antarctic and sub-Antarctic islands, available at public databases, resulted in that all the 11 specimens from Lutzow-Holm Bay possessed either of two major haplotypes detected in previous studies. It reflects the effective dispersal of the species between the localities including Lutzow-Holm Bay

First eumonostiliferous nemertean from the Nishi-Shichito Ridge, Genrokunemertes obesa gen. et sp. nov. (Eumonostilifera, Nemertea)

Nemerteans are mostly marine, benthic invertebrates, inhabiting intertidal to hadal zones. Recently, they have been recognized from deep sea with environmental DNA (eDNA) metabarcoding of sediment samples whereas any records from the locations and/or the water depth have not been documented in nemertean taxonomic publications to date. It suggests that there are major gaps between deep-sea nemertean fauna observed with eDNA and taxonomic knowledge. During a research expedition in 2021, we obtained a single specimen of eumonostiliferous nemertean from the southern part of Genroku Seamount Chain, the Nishi-Shichito Ridge, where any nemertean species have never been reported. Subsequent morphological and molecular examination reveal that the species is placed in a new genus and herein described as Genrokunemertes obesa gen. et sp. nov. It resembles shallow-water-dwelling Kurilonemertes and Typhloerstedia, but differs from the former in lacking eyes and the latter in possessing well-developed cephalic glands and lacking accessory nerves of lateral nerve cords. In terms of genetic distances based on partial sequences of the cytochrome c oxidase subunit I gene, G. obesa gen. et sp. nov. is closest to Monostilifera sp. Owase collected from Japan, which is characterized by large four eyes; the COI distance is higher than commonly observed interspecific divergences in eumonostiliferans

Three new species in Tetrastemma Ehrenberg, 1828 (Nemertea, Monostilifera) from sublittoral to upper bathyal zones of the northwestern Pacific

Monostiliferous nemerteans in the genus Tetrastemma Ehrenberg, 1828 are generally characterized as having four eyes, and they occur worldwide, from the intertidal zone to the deep-sea bottom. Recent extensive sampling of Tetrastemma has explored the high species diversity, including many undescribed forms, but phylogenic analysis has revealed non-monophyly of the genus. We herein describe three new species of the genus (T. album sp. nov., T. persona sp. nov., and T. shohoense sp. nov.) from northwestern Pacific waters based on specimens collected by dredging or by use of a remotely operated vehicle at depths of 116–455 m. Since anatomical and histological characters traditionally used in systematics of the genus are sometimes interspecifically uniform, a histology-free approach is applied for the species descriptions in this study. To confirm the generic affiliation of the new species, a molecular phylogenetic analysis based on partial sequences of cytochrome c oxidase subunit I, 16S rRNA, 18S rRNA, 28S rRNA, and histone H3 genes was performed. Our result shows that all three new species are nested in a subclade formed by species from the North Pacific and American Atlantic, inferring that geographic distribution does not reflect the cladogenesis of Tetrastemma. Furthermore, two Tetrastemma species with a cylindrical stylet basis, T. freyae Chernyshev et al., 2020 from off the coast of India and Hawaii and T. shohoense sp. nov. from Shoho Seamount, Japan, constitute a clade in the resulting tree