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We provide a review of the enoplid suborder Trefusiina Siddiqi, 1983, based on morphological considerations and analyses of new and published 18S rDNA sequences. We also describe Halanonchus scintillatulus Leduc sp. nov. from the Hauraki Gulf, northern New Zealand, as well as females of Trefusialaimus idrisi Leduc, 2013 from the continental slope of New Zealand. We show for the first time that the structure of the female reproductive system of Trefusialaimus Riemann, 1974 consists of two opposed and outstretched ovaries, an unusual feature for the Enoplida. The Trefusiina did not form a monophyletic group in the 18S rDNA phylogeny due to the placement of Lauratonema Gerlach, 1953 and Trefusialaimus sequences well away from the main Trefusiina clade. However, due to generally weak Maximum Likelihood support values, we refrain from changing the classification of these taxa until more comprehensive analyses can be conducted. Our phylogenetic analysis supports the inclusion of the Trischistomatidae Andrássy, 2007 within the Trefusiina, meaning that all of the enoplid suborders now include at least some terrestrial/freshwater representatives. The Trefusiina currently comprises five families, 14 genera and 92 valid species.
Rhaptothyreus is arguably the most enigmatic nematode taxon due to a combination of unusual morphological features (e.g., large feather-like amphids, vestigial mouth, trophosome, single spicule), unclear phylogenetic relationships (possible affinities with the Enoplida, Mermithida and Benthimermithida) and a distribution restricted to the deep sea. Here I provide the first record of the genus in the Western Pacific Ocean and describe new morphological features of a moulting juvenile. This specimen is characterised by features that differ markedly from those of the adults, the most prominent being the absence of cephalic sensillae and amphids and the presence of a stylet-like structure in the buccal cavity. Similar contrasts in morphology are found between adults and juveniles of the order Benthimermithida, which is characterised by free-living adults and parasitic juveniles.
Other morphological (large body size, presence of trophosome) and distributional characteristics (predominantly deep-sea distribution, juveniles rare / absent in sediments) are also common to both groups. Published records show that Rhaptothyreus is commonly found in oligotrophic environments (e.g., abyssal plain) where organisms bearing symbiotic bacteria are not typically found, which makes the presence of endosymbiotic bacteria inside the trophosome unlikely. These observations are consistent with the existence of a parasitic juvenile life stage in Rhaptothyreus.
The present study describes five new free-living nematode species and provides three new species records of the family Comesomatidae (genera Cervonema Wieser, 1954, Dorylaimopsis Ditlevsen, 1918, Hopperia Vitiello, 1969, and Kenyanema Muthumbi et al., 1997) from the continental margin of New Zealand, Southwest Pacific. Dichotomous identification keys are provided for all known species of Dorylaimopsis and Hopperia. Cervonema shiae Chen & Vincx, 2000 is recorded for the first time outside the type locality (Beagle Channel, Chile). C. kaikouraensis sp. nov. is characterised by amphideal fovea with 5.5 turns situated at 1.7 head diameter from anterior end, jointed outer labial setae, equal in length to cephalic setae, sperm dimorphism, and 5-6 small pre-cloacal supplements. C. multispira sp. nov. is characterised by amphideal fovea with 8.0-8.5 turns situated at 2.6-4.0 head diameter from anterior end, cephalic setae 2-3 μm long, slightly shorter than outer labial setae, presence of six uninucleated cells in males (potentially pseudocoelomocytes or supplementary excretory cells), 5 small pre-cloacal supplements, and strongly cuticularised, arcuate spicules with capitulum. C. proberti sp. nov. is characterised by amphideal fovea with 5 turns and located at < 1 head diameter from anterior end, cephalic setae 1.6-2.0 times longer than outer labial setae, and 8 small pre-cloacal supplements. Dorylaimopsis nodderi sp. nov. is characterised by cuticle with lateral differentiation consisting of three longitudinal rows of larger dots in the pharyngeal and caudal regions, two rows of larger dots in middle region of body, and spicules with rounded ventral projection at one third of spicule length from distal end, giving appearance of a joint. Hopperia ancora sp. nov. is characterised by short conical cephalic setae, spicules with hook-like projection at distal end, gubernaculum with bent apophyses, and 11-13 pre-cloacal supplements. H. beaglense Chen & Vincx, 1998 is recorded from Kaikoura Canyon, the fi rst record of this species outside the type locality (Beagle Channel, Chile). Kenyanema monorchis Muthumbi et al., 1997 is also recorded for the first time outside the type locality (Indian Ocean).
Two new genera and five new species of Selachinematidae are described from the New Zealand upper continental slope (350-1240 m depth). Synonchiella rotundicauda sp. nov. is characterised by cephalic setae 0.25 cbd long, mandibles each with two pairs of hooks and two wing-like projections laterally, eight cup-shaped pre-cloacal supplements and short rounded tail. Pseudocheironchus gen. nov. is similar to Cheironchus, but differs from the latter in having a cuticle without lateral differentiation, cephalic setae only slightly longer than the outer labial sensillae, and a posterior buccal cavity with three equal mandibles. Pseudocheironchus ingluviosus gen. et sp. nov. is characterised by mandibles with eight blunt teeth, multispiral amphideal fovea with five turns, and a short rounded tail. Males of this new species with 17-19 cup-shaped pre-cloacal supplements. Males of the genus Cobbionema are described for the first time; C. trigamma sp. nov. is characterised by four long cephalic setae and six smaller outer labial setae in one circle, six rhabdions surrounding the anterior buccal cavity, each with two pairs of pointed projections at their posterior extremities, posterior buccal cavity widening posteriorly, with three pairs of rhabdions fused posteriorly and widening anteriorly, males with two testes pointing anteriorly and with reflexed posterior testis, and no pre-cloacal supplements. Gammanema agglutinans sp. nov. is characterised by a short, stout body often covered in adhering mucus and detritus, cuticle with minute spines, leaf-shaped somatic setae with ducts, sexual dimorphism in the shape of the amphideal fovea (loop-shaped in males and spiral in females), posterior buccal cavity with three pairs of broad, column-shaped rhabdions fused anteriorly, intestine cells with orange-brown granules, and small tubular pre-cloacal supplements. Bendiella gen. nov. is most similar to Halichoanolaimus, but differs from the latter, and all other genera of the family Selachinematidae, in having a cuticle with lateral differentiation consisting of longitudinal rows of larger dots, and from all other genera of the Choniolaiminae in lacking pre-cloacal supplements. Bendiella thalassa gen. et sp. nov. is characterised by amphideal fovea with 5.25 turns, anterior buccal cavity with twelve rhabdions, each with a pair of pointed projections at posterior extremity, posterior buccal cavity with three Y-shaped pairs of slender rhabdions fused from two thirds of distance from anterior ends, and conico-cylindrical tail.
Two new species of the family Trefusiidae, viz., Trefusia piperata sp. nov. and Trefusialaimus idrisi sp. nov., are described from the crest of the Chatham Rise, Southwest Pacific Ocean (350 m water depth). The present study provides the first species records for this family in the region. Trefusia and Trefusialaimus comprise twenty and three valid species, respectively. A key to males of Trefusia is provided.
Litinium gludi sp. nov. (Nematoda, Oxystominidae) from Kermadec Trench, Southwest Pacific Ocean
(2021)
Recent work on the taxonomy of nematodes in Southwest Pacific Ocean trenches has led to the discovery of taxa which so far appear to be restricted to the oceans’ deepest environments. Here, Litinium gludi sp. nov. is described based on specimens obtained from a deep basin within the Kermadec Trench at 9540 m water depth. The new species differs from other species of the genus in having a conico-cylindrical tail, papillose labial sensilla, and heart- or leaf-shaped amphideal fovea. Both SSU and LSU phylogenetic analyses provide strong support for the placement of the new species within a clade containing both Thalassoalaimus and Litinum, and within Oxystomininae, which is consistent with the structure of the female reproductive system with only one posterior ovary in this subfamily. Our molecular analyses also indicate that the new species is most closely related to Thalassoalaimus despite lacking a caudal capsule, the main trait characterizing the latter genus, and despite being most morphologically similar to Litinium, particularly in the unusual shape of the amphideal fovea. However, given the changing definitions of the closely-related genera Thalassoalaimus and Litinium in recent years, available GenBank sequences may have been misidentified, which makes the interpretation of molecular phylogenetic analyses problematic. Given the current morphological definitions of Litinium and Thalassoalaimus, we choose to place the new species within Litinium, despite the apparently contradictory findings of molecular phylogenetic analyses. The placement of Cricohalalaimus in a clade with Thalassoalaimus and Litinium in both SSU and LSU analyses indicates that this genus should be placed within the Oxystomininae and not the Halalaiminae as in the current classification. This new proposed grouping is consistent with variation in the structure of the female reproductive system, a feature which appears more taxonomically informative than amphid shape for subfamily-level classification.
The Selachinematidae is a globally distributed family of predatory nematodes found from shallow waters to the abyssal plain. Here, three new species of Halichoanolaimus de Man, 1886 (H. ossilagulus sp. nov., H. funestus sp. nov. and H. pumilus sp. nov.) and one known species (H. ovalis Ditlevsen, 1921) are described from the New Zealand continental margin, thus bringing the total number of selachinematid species recorded from the New Zealand region to 14 and the total number of species of Halichoanolaimus to 26. The range of H. ovalis is extended from the Southern Ocean to the Southwest Pacific Ocean (latitude 42° S to 53° S); the depth range of this species, which was originally described from the littoral zone, is also extended to 1061 m depth. Dorsosublateral rows of pore complexes and pseudocoelomocytes, features that have either rarely or not been recorded previously in the genus, were observed in all four species described here. The taxonomic significance of these features remains to be ascertained for the family and will require observations of other species of Halichoanolaimus and selachinematid genera. Pseudocoelomocytes and pore complexes may have an excretory function, thus aiding to process the waste products of digestion in selachinematid taxa with a blind intestine.
Two new species of the family Desmodoridae are described from the upper continental slope of New Zealand, Southwest Pacific, and the genera Spirinia, Chromaspirina and Perspiria are revised. Spirinia verecunda sp. nov. is characterised by a short, stout body, cuticle covered in minute, hair-like structures, unispiral amphideal aperture and cryptospiral amphideal fovea, buccal cavity with small dorsal tooth and minute subventral teeth, eight oblong glands surrounding anterior portion of pharynx, large sperm cells, spicules with weak capitulum, and the absence of precloacal supplements. Stygodesmodora confusa sp. nov. is characterised by a relatively short body, spiral amphids with 1.2– 1.4 turns, cephalic setae situated at or slightly posterior to mid-level of amphid, and males with four precloacal supplements consisting of short setae on wide bases. Like other species of the genus, S. confusa sp. nov. is characterised by an annulated head region, but in some specimens the cuticle annulations are restricted to the dorsal and ventral sides of the head. S. confusa sp. nov. shows similarities with species of other desmodorid genera (i.e., Echinodesmodora, Bolbonema), but can be differentiated from them by the presence of an annulated head region and amphideal plates. The genera Spirinia, Chromaspirina and Perspiria have very similar morphologies and differ mainly in the size and structure of the buccal cavity (Spirinia vs Chromaspirina) or the shape of the tail and placement of the amphids relative to the cuticle annulations (Spirinia vs Perspiria); their diagnoses are clarified and some nomenclatural changes are proposed to eliminate overlap in the definitions of these genera.
Three new species of the order Monhysterida are described based on specimens obtained at depths of 8081 and 9177 m in the Kermadec Trench. Thelonema clarki sp. nov. is characterised by a large body size (3230–4461 μm), short cylindrical buccal cavity, gubernaculum without apophyses, and long conico-cylindrical tail. This is the first record of the genus since its original description over two decades ago from the Peru Basin. Metasphaerolaimus constrictus sp. nov. is characterised by a relatively long body (1232–1623 μm), slightly arcuate spicules without gubernaculum, and conico-cylindrical tail with inner cuticle conspicuously thickened immediately anterior to cylindrical portion. Monhystrella kermadecensis sp. nov. is characterised by a circle of papillose outer labial sensillae slightly anterior to the four short cephalic setae, gubernaculum with caudal apophyses, the presence of distinct cuticularised piece along anterior vaginal wall, and a relatively short conical (males) or conico-cylindrical tail (females) with conical, ventrally-curved spinneret. M. kermadecensis sp. nov. can be differentiated from all other species of the genus, and, indeed, the entire family, based on the variable position of the anterior gonad relative to the intestine. The new species is classified within the Monhysteridae, and not the closely-related Xyalidae, based on the small body size, a smooth cuticle, and the presence of six outer labial papillae and only one testis. Further work is required to clarify the placement of M. kermadecensis sp. nov. relative to other monhysterid genera. A tabular key to all ten valid Metasphaerolaimus species is presented.
Relatively little is known about the taxonomy and ecology of deep-sea nematode species inhabiting cold seep habitats. The available data show that cold seep nematode communities are typically characterized by low diversity and are often dominated by a single species, although no nematode taxon appears to have a strong association with methane seepage. In July 2019, a research voyage to New Zealand’s Hikurangi Margin provided an opportunity to characterize the nematode species communities of New Zealand cold seeps, which had not been investigated until now. Here, six new species and two new nematode genera of the class Chromadorea are described from macrofauna cores obtained at three seep sites (Mungaroa, Glendhu, and Uruti South) on Hikurangi Margin from 1227 to 2077 m depth. The species described here represent a wide range of feeding groups, ranging from deposit feeders (Linhomoeus pycnocricus sp. nov., Deraionema barbatum gen. et sp. nov.) to microvores (Aulostomonema abyssum gen. et sp. nov., Aegialoalaimus magnus sp. nov.) and epigrowth feeders (Desmodora parapilosa sp. nov.). The diet of Siphonolaimus curtisensillus sp. nov., which is characterized by an unusual stylet-like feeding apparatus, remains to be determined, however the presence of several different feeding modes in the species described here indicates that a range of food sources are exploited by macrofaunal nematodes at the study sites. Desmodora, Linhomoeus, and Aegialoalaimus have been reported from cold seep habitats previously, however no records of Siphonolaimus from cold seeps could be found in the literature. Aulostomonema gen. nov. does not appear to have a close association with seeps, whilst Deraionema gen. nov. appears to be restricted to the centre of the seep sites where methane seepage is likely strongest. Ongoing work on the ecology and distribution of nematode communities at the Hikurangi Margin seep sites will help determine spatial patterns in abundance and species distributions in more detail, including the identification of any species/taxa with affinities with methane seepage.