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

Amphimonhystrella

Key for identification of Amphimonhystrella species 1 Gubernaculum absent. Cuticle looks smooth. Cephalic and cervical setae 7–8 µm long............................................................................................... A. megastoma Timm 1961 ­ Gubernaculum present. Cuticle distinctly annulated. Cephalic and cervical setae less than 4 µm long.............................................................................................................. 2 2 Distal tips of spicules blunt ....................................................... A. unita Lorenzen 1977 ­ Distal tips of spicules pointed ......................................................... A. bullacauda sp. n.Published as part of Tchesunov, Alexei V. & Miljutina, Maria A., 2005, Three new minute nematode species of the superfamily Monhysteroidea from Arctic Abyss, pp. 19-32 in Zootaxa 1051 on page 22, DOI: 10.5281/zenodo.16998

Studies on Domorganus macronephriticus Goodey, 1947 (Nematoda: Ohridiidae)

The examination of Domorganus macronephriticus specimens isolated from soil samples from Germany and France, and from earthworms and soil in Russia revealed several previously unknown morphological features: (1) presence of two minute lateral tongues in the round lipless mouth opening; (2) absence of inner and outer labial papillae; (3) commalike amphids in the juveniles antedating the round amphids in adults; (4) ventral glands consisting of distinct canal and cell, with the gland body almost always situated on the right of the intestine; (5) presence of two large pseudocoelomocytes, located between the ventral gland body and the intestine; (6) presence of midventral prevulvar warts in the females, variable in size, number and position. In measurements and ratios females were more variable than males. The nematode lives as a commensal in the intestine of earthworms but is also commonly found free in soil. It is known to occur in various biotopes and soil types in six European countries.El estudio de ejemplares de Domorganus macronephriticus recogidos en muestras de suelo procedentes de Alemania y Francia, y de lombrices de tierra y suelo de Rusia, puso de manifiesto varios rasgos morfológicos antes desconocidos: i) presencia de dos lenguas diminutas laterales alrededor de la abertura bucal que carece de labios diferenciados; ii) ausencia de papilas labiales externas e internas; iii) anfidios con forma de coma en los individuos juveniles, que preceden a los anfidios redondeados de los adultos; iv) glándulas ventrales que constan de canal y célula, con el cuerpo glandular situado casi siempre sobre el lado derecho del intestino; v) existencia de dos grandes pseudocelomocitos, situados entre la glándula ventral y el intestino; vi) presencia de verrugas medioventrales prevulvares, que var.an en tamaño, número y posición. Las hembras fueron más variables en medidas e .índices. La especie vive como comensal en el intestino de lombrices de tierra pero se encuentra así mismo como forma de vida libre en el suelo con frecuencia. Se conoce su presencia en varios biotopos y tipos de suelo en seis países europeos

Amphimonhystrella Timm 1961

Amphimonhystrella Timm 1961 Xyalidae. Body very small (about 0.5 mm or less) and slender. Cuticle distinctly annulated or smooth, without lateral differentiation. Cephalic crown composed of ten (6 + 4) smooth setae, without additional setae. There may be scarce cervical and somatic setae along the body. Amphid large, round or slightly longitudinally oval. Esophastoma elongate conical to near cylindroid, with sclerotised rhabdions, surrounded with esophageal cuff. Esophagus slightly widening posteriad, without a terminal bulb. Renette cell not known. Prodelphic female gonad supplied with a postvulvar sac and to the left of midgut. Male gonads either paired (anterior outstretched testis to the left and posterior reflected testis to the right of midgut) or single anterior outstretched testis to the left of midgut. Spicules small, slightly bent, distally fused in one species (A. unita). Gubernaculum with small dorso­caudal apophysis or absent. Tail consists of proximal conical and distal cylindrical portions ending with terminal drop­shaped widening. Type species: Amphimonhystrella megastoma Timm 1961.Published as part of Tchesunov, Alexei V. & Miljutina, Maria A., 2005, Three new minute nematode species of the superfamily Monhysteroidea from Arctic Abyss, pp. 19-32 in Zootaxa 1051 on pages 21-22, DOI: 10.5281/zenodo.16998

Thalassomonhystera molloyensis Tchesunov et Miljutina, sp. n.

Thalassomonhystera molloyensis Tchesunov et Miljutina sp. n. Table 1, Figs 5 & 6 Material. One holotype male, four paratype males and two paratype females. The slides are deposited in the nematode collection of the Shirshov Institute of Oceanology of Russian Academy of Sciences, Moscow. Type locality. Arctic Ocean, area between Greenland and Svalbard, 79 ° 8.2 'N & 02° 53.6 'E, depth 5569 m (Molloy Deep), silt, 16 August, 2000. Etymology. Species name molloyensis is referred to the geographic area where the species was collected. Description. Body small and slender, elongate spindle­shaped. Cuticle thin and smooth. Cephalic end narrowed. Labial region set off slightly with labial sensilla as tiny papillae. Outer labial and cephalic setae very short, nearly equal and jointed in one crown of ten setae 1.5 –2.0 µm long (23–30 % c.b.d. in males, 23–25 % c.b.d. in females). Amphid circular, sometimes with slightly asymmetrical central spot, with distinct uninterrupted cuticular edging. In males, amphids are slightly larger than in females. Amphids situated well posterior to the stoma ending. There are two (males NN 1, 2, 3, 5, 6) or one (females NN 1, 4, 7) lateral or lateroventral cervical setae posterior to the amphid. There are usually one lateroventral seta just posterior to the nerve ring and a few sparse somatic setae along the body. Cervical and somatic setae 1–2 µm long. Buccal cavity cylindro­conoidal in shape and relatively voluminous. Esophastomal rhabdions slightly draw together to the posterior stoma ending or nearly parallel. Rhabdions thick but weakly sclerotised and weakly light­refracting, without an esophageal cuff. Esophagus with radial muscular striation, plainly widening to the posterior end. Cardia small, triangular, internal. Midgut with distinct peritrophic membrane and without visible intestinal cell borders. There may be a renette ampulla vaguely visible just posterior to the nerve ring and a renette cell body posterior to the cardia, to the right (males NN 2, 5, 6, females NN 4, 7, 8) or to the left (male N 3) of the intestine. Female gonad single, anterior, outstretched, situated entirely to the right of the intestine. Vagina strongly sclerotised. No postvulvar sac. Uterus may contain one ripe egg 24–27 µm long and 11.5–12.5 µm wide. Male gonad single, outstretched, situated to the left (males NN 1, 3) or to the right (males NN 2, 5, 6) of the midgut. Spermatozoa (or spermatides?) as tiny light­refracting granules. Spicules short, slightly arcuate, distally pointed and proximally cephalated with oblique knobs. Gubernaculum dense­bodied, with a dorso­caudal apophysis. There is a small ventral preanal papilla (or a pair of two close papillae?) situated slightly posterior to the level of the spicular knobs. A similar small ventral postanal papilla (or a pair of two close papillae) in the middle region of the tail. There are two or three preanal setae and three to four lateroventral, lateral and laterodorsal setae postanal setae on the male tail. Tail elongate conical, with terminal spinneret and caudal gland cell bodies within. In females, the tail usually bent dorsally. Discussion. Among Thalassomonhystera species, the new species is most similar to T. bathislandica Riemann 1995 also described from the north­eastern Atlantic abyssal (Riemann 1995). Both species are similar in minute body size and other dimensions as well as in rather voluminous stoma, position of amphids, renette cell and vulva, shape of the copulatory apparatus and tail. Also, both species show variable position of the male genital tract about the intestine, a deviation from the normal monhysterid morphology (Lorenzen 1978). T. molloyensis sp. n. differs from T. bathislandica by: 1) having a smaller body, male length 392–460 µm versus 572–684 µm, female length 376–472 µm versus 615–633 µm; 2) having a sclerotised lips of vulva; 3) the presense of two ventral papillae or pairs of papillae, first one in preanal position and second one in postanal position just behind the middle of the tail.Published as part of Tchesunov, Alexei V. & Miljutina, Maria A., 2005, Three new minute nematode species of the superfamily Monhysteroidea from Arctic Abyss, pp. 19-32 in Zootaxa 1051 on pages 29-30, DOI: 10.5281/zenodo.16998

Amphimonhystrella bullacauda Tchesunov et Miljutina, sp. n.

Amphimonhystrella bullacauda Tchesunov et Miljutina sp. n. Table 1, Figs 1, 2 Material. One holotype male, four paratype males and five paratype females. The slides are deposited in the nematode collection of the Shirshov Institute of Oceanology of Russian Academy of Sciences, Moscow. Type locality. Arctic Ocean, area between Greenland and Svalbard, 79 ° 8.2 'N & 02° 53.6 'E, depth 5569 m (Molloy Deep), silt, August 16, 2000. Etymology. The name bullacauda means “knob­terminated tail”. Description. Body slender, elongate spindle­shaped. Cuticle distinctly annulated with approximately ten annules per 10 µm. Cephalic end slightly narrowed, in shape of a truncated cone. Cephalic cuticle smooth from the apex to the stoma ending. There are very minute, obscure inner labial papillae in the labial region. Outer labial and cephalic setae united in almost one circle. Outer labial setae obscurely two­jointed and longer than smooth cephalic setae at about one third. Amphid relatively large, round or slightly longitudinally oval, with discontinuous fine but distinct edging, sometimes with central spot. There are no somatic setae visible along the body. Buccal cavity from elongateconical to nearly cylindroid, with thin but neat sclerotised walls, surrounded with an esophageal cuff at two thirds of its length. Esophagus slender but distinct, with weak radial muscular striation, slightly widened at the posterior end. Cardia cordate, vacuolised and surrounded with the intestinal tissue. There is no differentiated progaster or two­rowed arrangement of intestinal cells in the midgut. No renette cell visible. Single anterior female gonad situated to the left of the midgut. Female genital branch outstretched, poorly differentiated. The largest and ripest oocyte differs sharply from preceding oocytes by its greater size and dense coarse granulation. The ripest oocyte may reach 57–60 µm in length and 9–13 µm in width. Uterus plainly continues into a postvulvar sac narrowing to the blind posterior end situated ventrally of the intestine. A few spherical spermatozoa with minute central nuclei are present in the postvulvar sac. Single anterior male gonad outstretched and situated to the left of the midgut. Spermatocytes in the testis are very large and arranged in one row. There are no ripe spermatozoa found in the male gonad. No supplementary organs are present. Spicules very short, slightly arched, shaped as a curved dagger, distally acute and proximally slightly cephalated. Gubernaculum with a short dorso­caudal apophysis. Tail consists of a proximal conical portion sharply differentiated by a deep narrowing from terminal portion strongly enlarged in drop­like or clavate fashion. There are two or three very short terminal setae (1.5 µm) on the tail tip. No other setae on the tail. There are two caudal glands barely visible inside the tail and usually three separate caudal gland ducts with pores located at the terminal widening. Diagnosis. Amphimonhystrella bullacauda is similar to A. unita Lorenzen 1977, being of similar minute size (in A. unita, body length 485 µm in both male and female specimens), clearly annulated cuticle, absence of additional setae in cephalic crown, large longitudinal oval amphids, and prominent postvulvar sac with relatively large spermatozoa. However, A. bullacauda sp. n. differs from A. unita by having longer cephalic setae (1.5–3.5 versus 1.0 µm), lacking cervical setae, head set off the body, singular anterior testis, distally pointed spicules, much more protuberant terminal tail widening.Published as part of Tchesunov, Alexei V. & Miljutina, Maria A., 2005, Three new minute nematode species of the superfamily Monhysteroidea from Arctic Abyss, pp. 19-32 in Zootaxa 1051 on pages 22-25, DOI: 10.5281/zenodo.16998

Description of two free-living nematode species of Halomonhystera disjuncta complex (Nematoda: Monhysterida) from two peculiar habitats in the sea

Morphological descriptions of two Halomonhystera species (Nematoda, Monhysterida) are presented (Halomonhystera hermesi and Halomonhystera socialis). Halomonhystera hermesi sp. n. occurs in a dense monospecific and homogeneous population on bacterial mats in the HAyenkon Mosby mud volcano in the Barents Sea at a depth of 1,280 m. The species is an endemic lineage distinctly separated from other shallow-water cryptotaxa of the Halomonhystera disjucta species complex on the base of the mitochondrial gene cytochrome oxidase subunit I (genetic divergence 19.6-23.8 %) and nuclear genetic markers, and on the base of morphometrics by Van Campenhout et al. (2014). H. socialis (Butschli 1874) is redescribed on the basis of White Sea specimens. This species dwells in mass on the detached kelp accumulation in the upper sublittoral. H. socialis is differentiated from other species of the Halomonhystera disjuncta complex morphometrically by a larger body size and by genetic divergence in nuclear markers. The genus Halomonhystera Andrassy 2006 is redefined, and its morphospecies list is reviewed. Species H. bathislandica (Riemann 1995) comb. n., H. fisheri (Zekely et al. 2006) comb. n., H. islandica (De Coninck 1943) comb. n. and H. vandoverae (Zekely et al. 2006) comb. n. are transferred to Halomonhystera from Thalassomonhystera; H. paradisjuncta (de Coninck 1943) comb. n., H. rotundicapitata (Filipjev 1922) comb. n. and H. taurica (Tsalolikhin 2007) comb. n. transferred to Halomonhystera from Geomonhystera. Halomonhystera ambiguoides (Butschli 1874) is considered as species inquirenda because of incompleteness of its diagnosis

Draconematinae Filipjev 1918

Subfamily Draconematinae Filipjev, 1918 <p> <b>Diagnosis</b> (emend. after Lorenzen 1994; Allen & Noffsinger 1978; Decraemer <i>et al</i>. 1997): Draconematidae. Body clearly swollen in pharyngeal and midbody regions with distinct narrowing between them. Pharynx dumbbell-shaped, i.e. swollen anterior corpus and posterior bulb with isthmus between them. Buccal cavity small and unarmed.</p> <p> Type genus: <i>Draconema</i> Cobb, 1913.</p>Published as part of <i>Fedyaeva, Maria A., Neretina, Tatjana V., Konovalova, Olga P. & Tchesunov, Alexei V., 2016, Two known and one new species of Draconematidae and Epsilonematidae (Nematoda, Desmodorida) from the White Sea, North Russia, pp. 383-411 in Zootaxa 4121 (4)</i> on page 386, DOI: 10.11646/zootaxa.4121.4.2, <a href="http://zenodo.org/record/265069">http://zenodo.org/record/265069</a&gt

Prochaetosoma Micoletzky 1922

Genus <i>Prochaetosoma</i> Micoletzky, 1922 <p> <b>Diagnosis</b> (after Allen & Noffsinger 1978; Decraemer <i>et al</i>. 1997, emended): Prochaetosomatinae. Pharyngeal body region only slightly swollen. Rostrum rounded. Six to 14 CATs located just posterior to rostrum. Amphideal fovea loop-shaped to uni- or doubled spiral. PATs all anterior to anus. Pharynx consists of cylindrical corpus and posterior bulb; internal cuticle of the bulb distinctly thickened in most species. Buccal cavity with conspicuous dorsal tooth.</p> <p> Type species: <i>Prochaetosoma primitiva</i> (Steiner, 1916) Micoletzky, 1922.</p> <p> <b>Discussion.</b> In their synthesis of Draconematidae, Decraemer <i>et al</i>. (1997) listed ten species of <i>Prochaetosoma</i>. Some of these species, <i>i.e</i>. <i>P. arcticum</i> (Kreis, 1963), <i>D. lugubre</i> (Gerlach, 1957) and <i>P. primitivum</i> (Steiner, 1916) are known from only a few or a single female and juveniles. The lack of males in the original diagnoses hampers identification because the males, apart from the copulatory apparatus important for species determination, may possess particular precloacal midventral differentiations indicating belonging to a definite species. Therefore, since diagnoses of <i>P. arcticum</i> and <i>P. lugubre</i> miss male characters, and their females are not marked by any clear diagnostic features, both these species are qualified here as <i>species inquirendae</i>. They may be restored as valid species in future if males and females found and re-described from type localities. Decraemer <i>et al.</i> (1997) regarded <i>P. primitivum</i>, the type species of <i>Prochaetosoma</i> Micoletzky, 1922, despite the lack of males, since the single fourth stage juvenile specimen described distinctive characters such as the number of posterior adhesive tubes.</p> <p> Rho <i>et al</i>. (2010) described <i>P. dokdoense</i>, summarized eleven valid species of <i>Prochaetosoma</i> and provided a table and a key for their identification. Almost simultaneously, Rho & Min (2011) described eight additional species (<i>P. beomseomense</i> Rho & Kim, <i>P. brevicaudatum</i> Rho & Kim, <i>P. byungilli</i> Rho & Kim, <i>P. cracense</i> Rho & Kim, <i>P. saheungi</i> Rho & Kim, <i>P. sujungi</i> Rho & Kim, <i>P. supseomense</i> Rho & Kim, <i>P. youngdeokense</i> Rho & Kim). As in the case of <i>Draconema</i> (see above), these species names are accompanied neither with designation of new species nor indication of a former publication of the species. Again, we treat these eight species as invalid.</p>Published as part of <i>Fedyaeva, Maria A., Neretina, Tatjana V., Konovalova, Olga P. & Tchesunov, Alexei V., 2016, Two known and one new species of Draconematidae and Epsilonematidae (Nematoda, Desmodorida) from the White Sea, North Russia, pp. 383-411 in Zootaxa 4121 (4)</i> on page 393, DOI: 10.11646/zootaxa.4121.4.2, <a href="http://zenodo.org/record/265069">http://zenodo.org/record/265069</a&gt