Thalassomermis megamphis n. gen., n. sp. (Mermithidae: Nemata) from the Bathyal South Atlantic Ocean

Thalassomermis megamphis n. gen., n. sp. (Mermithidae: Nemata) was extracted from sediment collected off the coast of Brazil at a depth of approximately 1,000 m. Although the food of this new nematode is unknown, the reduction of the stoma and esophagus and presence of a trophosome indicate that it is parasitic in its juvenile stages. Thalassomermis megaraphis n. gen., n. sp. is assigned to Mermithidae because of its similarity to that family in the appearance of the cephalic sensory receptors, the long and tubular vagina, and copulatory muscles of the male extending posteriorly throughout most of the length of the tail. Thalassomermis megamphis n. gen., n. sp. differs from all other members of Mermithidae by the large, lenticular, intracuticular amphidial fovea with coiled, emergent terminal filaments as well as the small amphidial aperture situated over the center of the fovea.     

Quantitative distribution of meiobenthos and the structure of the free-living nematode community of the mangrove intertidal zone in Nha Trang bay (Vietnam) in the South China Sea

Meiobenthic studies were performed in an intertidal area in the Be River estuary (Nha Trang Bay, Vietnam). The study area is an area of riverine-type mangroves that have been heavily damaged by human impacts, including timber cutting and waste. Three biotopes are situated in the middle intertidal zone: a fringe of Rhizophora stylosa, a bush area composed of Avicennia aff. alba behind it, and muddy sand with fiddler crabs (Uca spp.), which is free of mangrove plants. Three replicate samples of meiobenthos were collected in each biotope and each sample was subdivided into two layers: 0–1 and 1–4 cm. The abundance of metazoan meiobenthos varied from 735 specimens/10 cm² in the Uca spp. biotope to 244 specimens/10 cm² beneath the Rhizophora trees. Six taxonomic groups of high rank were found among the meiofauna: Nematoda, Copepoda (Harpacticoida), Oligochaeta, Turbellaria, Kinorhyncha, and Foraminifera (Allogromiida). The spatial variability of meiobenthos and its key taxa was estimated and the spatial distribution patterns of free-living nematode species were described. About 90% of the total meiobenthos inhabited the upper 0–1 cm of the sediments. Nematodes constituted 90–95% of all meiobenthic organisms in the samples. A total of 48 species of free-living nematodes were found in the investigated mangrove intertidal area. In terms of species composition and set of dominants, the nematode community is comprised of three local assemblages: one of them inhabits the uppermost centimeter in the Uca and Avicennia biocenoses; the second assemblage occupies the upper sediment layer in the Rhizophora stand; a less abundant but specific assemblage of several nematode species occurs in the subsurface sediments at all three sites.     

Meiofauna in the Gollum Channels and the Whittard Canyon, Celtic Margin--how local environmental conditions shape nematode structure and function

The Gollum Channels and Whittard Canyon (NE Atlantic) are two areas that receive high input of organic matter and phytodetritus from euphotic layers, but they are typified by different trophic and hydrodynamic conditions. Sediment biogeochemistry was analysed in conjunction with structure and diversity of the nematode community and differences were tested between study areas, water depths (700 m vs 1000 m), stations, and sediment layers. The Gollum Channels and Whittard Canyon harboured high meiofauna abundances (1054-1426 ind. 10 cm(-2)) and high nematode diversity (total of 181 genera). Next to enhanced meiofauna abundance and nematode biomass, there were signs of high levels of organic matter deposition leading to reduced sedimentary conditions, which in turn structured the nematode community. Striking in this respect was the presence of large numbers of 'chemosynthetic' Astomonema nematodes (Astomonema southwardorum, Order Monhysterida, Family Siphonolaimidae). This genus lacks a mouth, buccal cavity and pharynx and possesses a rudimentary gut containing internal, symbiotic prokaryotes which have been recognised as sulphur-oxidising bacteria. Dominance of Astomonema may indicate the presence of reduced environments in the study areas, which is partially confirmed by the local biogeochemical environment. The nematode communities were mostly affected by sediment layer differences and concomitant trophic conditions rather than other spatial gradients related to study area, water depth or station differences, pointing to small-scale heterogeneity as the main source of variation in nematode structure and function. Furthermore, the positive relation between nematode standing stocks, and quantity and quality of the organic matter was stronger when hydrodynamic disturbance was greater. Analogically, this study also suggests that structural diversity can be positively correlated with trophic conditions and that this relation is tighter when hydrodynamic disturbance is greater.     

Nematode assemblages from the Kandalaksha Depression (White Sea, 251–288 m water depth)

The shallow-water nematodes of the White Sea are relatively well studied; however, information on the nematode fauna inhabiting the deepest part of this sea is very scarce. The composition of the nematode assemblages (at species and genus level) was studied in samples collected during four sampling occasions in the deepest part of the Kandalaksha Depression (the White Sea) in July 1998, October 1998, May 1999, and November 1999. Samples were collected from a depth of 251–288 m with the aid of a multicorer. In total, 59 nematode morphotypes belonging to 37 genera and 18 families were distinguished. The genera Sabatieria and Filipjeva dominated at all stations, followed by Aponema, Desmoscolex, and Quadricoma. The composition of the dominant genera can be considered typical for this depth range in temperate and Arctic waters, although Filipjeva and Aponema were among the dominant genera for the first time. The most abundant species were Sabatieria ornata, Aponema bathyalis, and Filipjeva filipjevi. In general, diversity of the nematode assemblages was lower than in the temperate and Arctic continental shelf and slope with reduced evenness and species richness. The evenness of nematode assemblages and other diversity indices decreased with increasing sediment depth. Based on the valid species and genera recorded, the nematode fauna of the Kandalaksha Depression showed a higher resemblance to that found in the shallow waters of Kandalaksha Bay.     

Viable Nematodes from Late Pleistocene Permafrost of the Kolyma River Lowland

We have obtained the first data demonstrating the capability of multicellular organisms for longterm cryobiosis in permafrost deposits of the Arctic. The viable soil nematodes Panagrolaimus aff. detritophagus (Rhabditida) and Plectus aff. parvus (Plectida) were isolated from the samples of Pleistocene permafrost deposits of the Kolyma River Lowland. The duration of natural cryopreservation of the nematodes corresponds to the age of the deposits, 30 000–40 000 years.     

The Halomonhystera disjuncta population is homogeneous across the Håkon Mosby mud volcano (Barents Sea) but is genetically differentiated from its shallow‐water relatives

The deep sea has a high biodiversity and a characteristic bathyal fauna. Earlier evidence suggested that at least some shallow‐water species invaded the ecosystem followed by radiation leading to endemic deep‐sea lineages with a genetic and/or morphological similarity to their shallow‐water counterparts. The nematode Halomonhystera disjuncta has been reported from shallow‐water habitats and the deep sea [Håkon Mosby mud volcano (HMMV)], but the morphological features and the phylogenetic relationships between deep‐sea and shallow‐water representatives remain largely unknown. Furthermore, nothing is known about the genetic structure of the H. disjuncta population within the HMMV. This study is the first integrative approach in which the morphological and phylogenetic relationships between a deep‐sea and shallow‐water free‐living nematode species are investigated. To elucidate the phylogenetic relationships, we analysed the mitochondrial gene Cytochrome oxidase c subunit I (COI) and three nuclear ribosomal genes (Internal Transcribed Spacer region, 18S and the D2D3 region of 28S). Our results show that deep‐sea nematodes comprise an endemic lineage compared to the shallow‐water representatives with different morphometric features. COI genetic divergence between the deep‐sea and shallow‐water specimens ranges between 19.1% and 25.2%. Taking these findings into account, we conclude that the deep‐sea form is a new species. amova revealed no genetic structure across the HMMV, suggesting that nematodes are able to disperse efficiently in the mud volcano.     

Free-living nematodes of the genus <Emphasis Type="Italic">Alaimella</Emphasis> Cobb 1920 (Nematoda: Leptolaimidae): A description of <Emphasis Type="Italic">A. macramphis</Emphasis> sp. n. from the White Sea and a revision of the genus

Alaimella cincta Cobb 1920 and Alaimella macramphis sp. n. are described and illustrated. Both the species were first recorded for the White Sea in northern Russia. A. cincta occurs in the shells of the agglutinated foraminiferan Reophax curtus, as well as freely in bottom sediments. A. macramphis sp. n. is described from a single male sampled from bottom sediments. A. macramphis sp. n. is distinguished from two previously known species of Alaimella (A. cincta Cobb 1920 and A. truncate Cobb 1920) by having a longer body, longer cephalic setae, and a wide amphid equal to the respective body diameter. The new species also differs from A. truncate by the distinct striation of the cuticular annulations. The Alaimella species are additionally characterized by having a posterior glandular widening of the esophagus. An emended diagnosis of the genus Alaimella Cobb 1920 and a key for species identification are provided.     

Benthic meiofaunal density and community composition in the deep White Sea and their temporal variations

In spite of the fact that shallow-water meiobenthos of the White Sea is a relatively well studied, the information on meiobenthic fauna from the deepest part of this sea is still very scanty. This study represents the first major study of the meiobenthos from the deep White Sea. The composition of the meiobenthic community, density and vertical distribution was studied during four sampling occasions in the deepest part of the Kandalaksha Depression (White Sea) in July 1998, October 1998, May 1999 and November 1999. Samples were collected from a depth of 270?m with the aid of a multicorer. The total density of meiobenthos in 1998 was twice than in 1999 (on average, 2,356 and 1,464 ind./10?cm², respectively). The most abundant meiobenthic group was Foraminifera (59?%), followed by Nematoda (26?%) and Harpacticoida (7?%). These relative and absolute abundance values are comparable with the same depth interval in Arctic and temperate regions. The density of foraminiferans and nematodes was higher in the autumn and lower in the summer. This may be explained by the mass propagation of these animals in the autumn season: the density of juvenile nematodes and small-sized foraminiferans increased significantly in the 1- to 4-cm-deep sediment layers in autumn. The size range of the meiobenthos in the deepest part of the White Sea was also comparable to deep-sea meiobenthos (the 63–125 and 125–250?μm size classes were most dominant).