No abstract

Tetrastemma Ehrenberg, 1828, is one of the most speciose (~110 spp.) genera within the phylum Nemertea, comprising marine monostiliferans generally having four eyes. Monophyly of Tetrastemma remains open to question, having been tested to date only with 18S rRNA gene sequences targeting 13 species. Here, we examine the clade Tetrastemma with additional gene markers (18S rRNA, 28S rRNA, histone H3, 16S rRNA, and cytochrome c oxidase subunit I genes) and OTUs (66 specimens representing 53 species in Tetrastemma), along with a taxon sampling covering the entire Eumonostilifera. Our analysis revealed that Tetrastemma (a) as non‐monophyletic (as were Tetrastemmatidae) (b) contains a major clade consisting of four geographically cohesive subclades, whereas (c) Tetrastemma arcticum Uschakov, 1926; Tetrastemma bilineatum Coe, 1904; Tetrastemma vittigerum (Bürger, 1904); Tetrastemma wilsoni Coe, 1943; and two specimens tentatively identified as Tetrastemma sp. occur outside this major clade, and iv) the three species of Psammamphiporus Gibson, 1989, and Quasitetrastemma Chernyshev, 2004, nest within in the major Tetrastemma clade. Thus, we (a) synonymize Psammamphiporus and Quasitetrastemma with the senior name Tetrastemma and (b) establish Arctostemma gen. nov. for T. arcticum to yield Arctostemma arcticum (Uschakov, 1926) comb. nov.

The Kuril Basin and the Kuril-Kamchatka Trench are two interconnected deep-sea ecosystems both located in one of the most highly productive regions of the world’s oceans. The main distinguishing features of these deep-sea ecosystems are the low oxygen concentration in the near-bottom water in the Kuril Basin, and the high hydrostatic pressure in the trench. We investigated the abundance of meio- and macrobenthic nematodes and macrofauna on the Kuril Basin floor (depths of 3,300–3,366 m) and in the Kuril-Kamchatka Trench area (depths of 3,432–9,539 m), as well as the influence of some environmental factors on the quantitative distribution of bottom fauna. This was not studied so far. The study also focused on the species composition and quantitative distribution of Polychaeta and Bivalvia, which were dominant in abundance among macrofaunal samples. The main factors influencing the quantitative distribution of macrofauna and nematodes were depth, oxygen concentration, and structure of bottom sediments. The Kuril Basin bottom communities are characterized by a high abundance of nematodes and macrofauna, a high species richness of polychaetes, and a pronounced dominance of small-sized species of Polychaeta and Bivalvia, which are probably more tolerant to low oxygen concentrations. Compared to the Kuril Basin, the Kuril-Kamchatka Trench area (at depths of 3,432–5,741 m) had a more diverse and abundant macrofauna, and a very high abundance of meio- and macrobenthic nematodes. In the trench (at depths more than 6,000 m), the diversity of macrofauna and the abundance of macrobenthic nematodes decreased, while the abundance of macrofauna increased with increasing depth. On the trench floor, the macrofaunal abundance was highest due to the high density of populations of several bivalve and polychaete species, apparently adapted to the high hydrostatic pressure on the trench floor. Obviously, the high primary production of surface waters supports the diverse and abundant deep-sea bottom fauna in the studied areas of the northwestern Pacific. Furthermore, a large number of animals with chemosynthetic endosymbiotic bacteria were found in the bottom communities of the Kuril Basin and the Kuril-Kamchatka Trench. This suggests a significant contribution of chemosynthetic organic carbon to functioning of these deep-sea ecosystems.

Tetrodotoxin (TTX) is a potent neurotoxin found in many marine and terrestrial animals, but only a few species, such as the ribbon worms of the genus Cephalothrix, accumulate it in extremely high concentrations. The intrabody distribution of TTX in highly toxic organisms is of great interest because it helps researchers to understand the pathways by which the toxin migrates, accumulates, and functions in tissues. Using immunohistochemistry with anti-TTX antibodies, the authors of this study investigated the toxin’s distribution inside the organs, tissues, and cells of Cephalothrix cf. simula. The cell types of TTX-positive tissues were identified by light microscopy. The main sites of TTX accumulation occurred in the secretory cells of the integuments, the microvilli of the epidermal ciliary cells, cephalic glands, the glandular epithelia of the proboscises, the enterocytes of the digestive systems, and nephridia. Obtained data suggest the toxin migrates from the digestive system through blood vessels to target organs. TTX is excreted from the body through the nephridia and mucus of epidermal cells.

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.

No abstract

No abstract

At present, the collection of the Zoological Institute contains 29 type specimens of 23 species of pelagic nemerteans from the orders Pelagica and Cratenemertea. The types of four species (Pelagonemertes laticauda Korotkevitsch, 1955, P. oviporus Korotkevitsch, 1955, Obnemertes maximovi Korotkevitsch, 1960 and O. ramosa Korotkevitsch, 1960) have not been found. The lectotype for Mesarmaueria pellucida Korotkevitsch, 1955 is designated. The genus Nemertobus Chernyshev, 1992 is synonymized with Obnemertes Prudhoe, 1963. Nectonemertes compacta Korotkevitsch, 1964 and Pelagonemertes parvula Korotkevitsch, 1964 are transferred to Chuniella Brinkmann, 1917 and Balaenanemertes Bürger, 1909, respectively.