Cephalic Setae Research Articles

Two new species of Microlaimidae (Nematoda: Microlaimida) from the Continental Shelf off Northeastern Brazil (Atlantic Ocean) with emended diagnosis and dichotomous key

New species of the genera Spirobolbolaimus and Ixonema (Nematoda: Microlaimidae) have been found in sediment samples collected in the South Atlantic, along the Continental Shelf break off Northeastern Brazil. Different to other Spirobolbolaimus species, S. pernambucanus sp. nov. possesses six outer labial setae and four cephalic setae with approximately the same length. Ixonema gracieleae sp. nov. differs from other species of Ixonema in having somatic setae on peduncles. This is the first time that new species of these taxa have been described for the Brazilian coast. An amendment of the diagnosis and a dichotomous key are proposed for both genera.

Two new species of Nematoda: Gairleanema pulchra sp. nov. (Tripyloididae) and Axonolaimus dimorphous sp. nov. (Axonolaimidae) from the Yellow Sea, China

Two new species of Nematoda, Gairleanema pulchra sp. nov. and Axonolaimus dimorphous sp. nov. are described from Rizhao coast, the Yelllow Sea. Gairleanema pulchra sp. nov. is characterized by six inner labial setae with bulbous swelling, six long outer labial setae and four short cephalic setae in one circle, amphidial fovea oval-shaped, spicules L-shaped with proximal end slightly cephalated, gubernaculum boat shaped with proximal end hooked anteriorly, seven oval-shaped precloacal supplements and tail conico-cylindrical. With the species description here two species are considered valid now in genus Gairleanema. Axonolaimus dimorphous sp. nov. is characterized by four long cephalic setae, amphidial fovea elongated loop in males and loop-shaped in females, spicules arcuated, gubernaculum with dorsal apophysis slightly directed to caudal position and tail conico-cylindrical with caudal setae. With the species description here 34 species are considered valid now in genus Axonolaimus.

Two new species of the order Monhysterida (Nematoda) from the sea of China.

Two new marine nematode species belonging to the order Monhysterida are described from the sea of China. Halomonhysterazhangisp. nov. is characterized by its relatively small body size; short anterior sensory setae; small, circular amphidial fovea located at the level of buccal cavity base; funnel-shaped buccal cavity; an excretory-secretory system with a large ventral gland and opening as a very narrow canal just posterior to the level of cephalic setae; slightly curved slender spicules with cephalated proximal end and tapered distal end; rod-like gubernaculum without apophysis; two papilliform precloacal supplements just in front of the cloaca; conico-cylindrical tail with two ventral papillae, each with a seta; and distance between the vulva and anus slightly longer than the tail length. This is the first new species of epiphytic nematode reported in China. The second new species, Stylotheristusflagellicaudatussp. nov., has a relatively shorter body and longer tail; striated cuticle; The anterior sensilla arranged in two circles, the first circle consisting of six inner labial setiform papillae (3-4 µm) and the second circle consisting of 16 long setae (12-19 µm); a transversely oval amphideal fovea; a well-developed muscle around the funnel-shaped buccal cavity; short spicules and a gubernaculum composed of a single piece; and precloacal supplements absent. An updated key to all species of Halomonhystera and pictorial key to all species of Stylotheristus are also given.

Two new species of Hypodontolaiminae (Nematoda, Chromadorida, Chromadoridae) from the Yellow Sea with a phylogenetic analysis in the subfamily.

Two new species of Hypodontolaiminae, Dichromadoramediasp. nov. and Neochromadoraparabilineatasp. nov., were isolated and described from the Yellow Sea, China. Dichromadoramediasp. nov. is characterized by four long cephalic setae, the amphidial fovea transverse oval in the male and slit-shaped in the female, the pharynx with a single posterior bulb, spicules curved and distally bifurcated, gubernaculum jointed, four (1+3) precloacal supplements papilliform, and the tail conical elongated with a short spinneret. Neochromadoraparabilineatasp. nov. is characterized by the buccal cavity with one large hollow dorsal tooth and two small subventral teeth, the pharynx with an obvious posterior bulb, spicules L-shaped and widened medially, gubernaculum boat-shaped, seven cup-shaped and equidistant precloacal supplements, and a long and gradually tapering tail. The phylogenetic analysis of maximum likelihood and Bayesian inference based on rDNA sequences confirmed the taxonomic positions of Neochromadoraparabilineatasp. nov. and Dichromadoramediasp. nov. within Hypodontolaiminae. Tree topology in Hypodontolaiminae shows the genera Neochromadora, Dichromadora, Ptycholaimellus, and Spilophorella as polyphyletic groups, and the genus Chromadorita as a paraphyletic group.

Two new species of Sabatieria de Rouville, 1903 (Nematoda: Araeolaimida: Comesomatidae) from the Southern Ocean.

Two new free-living marine nematode species of the genus Sabatieria de Rouville, 1903 are described from the Southern Ocean using morphological and molecular data. Sabatieria brevicaudata sp. nov. is characterized by body length 14761740 m, short cephalic setae, 1324% corresponding body diameter long, lateral differentiation of body cuticle with only slightly coarser punctations, spiral amphidial fovea with 3 turns, spicules arcuated and 1.31.6 cloacal body diameter long, slightly arcuated gubernacular apophyses, and twelve precloacal supplements, in the form of small pores. Sabatieria multipora sp. nov. is characterized by body length 21392324 m, short cephalic setae (47 m long, 3040% corresponding body diameter long), cuticle with lateral differentiation of distinctly coarser punctations extending from anterior edge of amphidial fovea to anterior of intestine and in the tail region, spiral amphidial fovea with 3 turns, males with spicules 1.92.0 cloacal body diameter long, seventeen fine tubular precloacal supplements with distance between adjacent supplements increasing towards anterior, and with curved gubernacular apophyses. We obtained 18S rDNA and 28S rDNA sequences from the two new species, which are both closely related to other species of Sabatieria. Our analyses also show that several genera of Comesomatidae Filipjev, 1918 do not form monophyletic clades.

Three New Species of Free-Living Marine Nematodes of the Order Enoplida Filipjev, 1929 (Nematoda) from the Yellow Sea, China

Three new nematode species belonging to the order Enoplida were discovered in the muddy and sandy sediment along the Shandong peninsula coast of the Yellow Sea during a biodiversity investigation of marine nematodes in the Yellow Sea. They are named Belbolla octobulba sp. nov., Ironella gracilis sp. nov. and Oxystomina longiseta sp. nov. Belbolla octobulba sp. nov. is characterized by having eight pharyngeal bulbs; spicules arcuate, broad and even; gubernaculum with a pair of dorso-caudal apophyses, about a third of the length of spicule; and two winged precloacal supplements. Ironella gracilis sp. nov. differs from known species by body slender, buccal cavity divided into conical vestibulum and cylindrical posterior portion, three sclerotized teeth located in the vestibulum; both circles of outer labial setae and cephalic setae 10 µm apart; elongated spicules weakly arcuate with central strip and cephalate proximal end; gubernaculum conical without apophysis; and a tubular precloacal supplement with a long seta at its anterior end. Oxystomina longiseta sp. nov. can be distinguished from other known species by the relatively long outer labial setae and cephalic setae; arcuate spicules expanded proximally with a median rib; gubernaculum small and oblong; and two unequal precloacal supplementary setae, anterior one short, posterior one very long. Updated keys to eighteen species of Belbolla and keys to four species of Ironella are given.

Two new species of Xyalidae Chitwood, 1951 (Nematoda, Monhysterida) from Chinese Sea Area.

Two new nematode species of the family Xyalidae were found in the intertidal zone of the Chinese coast, and they are described here as Daptonema sinica sp. nov. and Metadesmolaimus bulbosus sp. nov. Daptonema sinica sp. nov. is characterised by a relatively large body with a broad funnel-shaped buccal cavity; relatively long cephalic setae; a circular amphidial fovea posterior to the buccal cavity; slender spicules bending into a hook shape in the posterior half; a small plate-like gubernaculum without apophysis; and a conico-cylindrical slender tail with terminal setae. Metadesmolaimus bulbosus sp. nov. can be identified by its large buccal cavity, long cervical setae, multiple bulb-like pharyngeal muscular swellings, conico-cylindrical tail narrowing abruptly immediately posterior to the cloaca, straight clavated spicules with a broad proximal end and hooked distal end, and gubernaculum absent. An updated dichotomous key to the species of Metadesmolaimus is given.

Two New Nematode Species, Desmolaimus magnus sp. nov. (Monhysterida, Linhomoeidae) and Metadesmolaimus robustus sp. nov. (Monhysterida, Xyalidae), from the Yellow Sea, China with Phylogenetic Analyses within Linhomoeidae and Xyalidae

Two new species are described from the Rizhao coast along the Yellow Sea. Desmolaimus magnus sp. nov. is characterized by its relatively large body size, faintly striated cuticle, four long cephalic setae, a wide buccal cavity with cuticularized transverse rings, an amphidial fovea at the junction of the buccal cavity and pharynx, a pharynx without a bulb, curved spicules, a gubernaculum with a dorso–caudal apophysis, and an elongated conical tail. Metadesmolaimus robustus sp. nov. is characterized by its relatively large body size, coarsely striated cuticle, spacious buccal cavity with cuticularized rings, six inner labial sensilla setiform, six outer labial setae, and four long cephalic setae. The pharynx is notably muscularized, and the spicules are straight and jointed with a slightly swollen proximal end and a hooked distal end. The gubernaculum is brownish and comma–shaped, and the tail is conico–cylindrical with terminal setae. Phylogenetic analyses using maximum–likelihood and Bayesin inference, based on small subunit and D2–D3 fragment of large subunit rDNA sequences, place Desmolaimus magnus sp. nov. within the framework of the family Linhomoeidae and Metadesmolaimus robustus sp. nov. within Xyalidae. Topology trees at the family level show genera Desmolaimus and Metadesmolaimus as paraphyletic groups, the genus Terschellingia as a monophylectic group, the genus Theristus as a monophylectic group based on SSU sequence, the genus Daptonema as a monophylectic group based on LSU sequence.

Description of Bolbolaimus major sp. nov. (Nematoda), from the Yellow Sea, China and phylogenetic analysis in Microlaimidae.

Bolbolaimus major sp. nov. is described from Rizhao coast along the Yellow Sea. The new species is characterized by relatively large body size, cuticle strongly annulated, six outer labial sensilla setiform, four cephalic setae long, buccal cavity wide with one large dorsal tooth and two small subventral teeth, amphidial fovea unispiral shaped oval in males and circular in females, spicules curved with swollen proximal end, gubernaculum with anterior-hooked dorso-caudal apophysis, and tail conical with short spinneret. A phylogenetic analysis of maximum-likelihood and Bayesin inference based on rDNA sequences confirms the taxonomic position of Bolbolaimus major sp. nov. within the family Microlaimidae. Tree topology in Microlaimidae shows genus Microlaimus as polyphyletic group and genera in Microlaimidae are closely related.

Description of a new nematode species, Chromadorinacommunis sp. nov. (Nematoda, Chromadoridae), from Changdao Island, China and phylogenetic analysis of Chromadorida based on small subunit rRNA gene sequences.

Chromadorinacommunissp. nov. is described from Changdao Island at the confluence of the Yellow and the Bohai seas. The new species is characterized by its medium-sized body; finely striated cuticle with homogeneous punctations; absence of ocelli; buccal cavity with three equal-sized, solid teeth; four cephalic setae; oval amphidial fovea which is positioned between cephalic setae; curved spicules with tapered distal ends; simple, boat-shaped gubernaculums; five or six cup-shaped precloacal supplements; and conical tail with a very short spinneret. A phylogenetic analysis of small subunit rRNA gene sequences using maximum-likelihood and Bayesin inference confirmed the taxonomic position of Chromadorinacommunissp. nov. within Chromadorinae. Tree topology in Chromadorida shows six morphological families clustered into a monophyletic clade and verifies the taxonomic position of the family Neotonchidae based on morphological and molecular analysis.

Descriptions of Leptolaimus sinensis sp. nov. and Perspiria brevicaudata sp. nov. (Nematoda) from the Yellow Sea, China

Two new free-living marine nematodes which were collected at silt beach of Rizhao along the Yellow Sea are identified here as Leptolaimus sinensis sp. nov. and Perspiria brevicaudata sp. nov. Leptolaimus sinensis sp. nov. is characterized by annulated cuticle with lateral alae, 2 µm in width; buccal cavity cylindrical; cephalic setae 2 µm long; amphidial fovea unispiral, circular in outline; six to seven evenly spaced tubular precloacal supplements and 23-29 continuous alveolar supplements extending from cloaca to level of the base of buccal cavity; spicules slender, slightly arcuate; gubernaculum with dorso-caudal apophysis; tail conico-cylindrical, about 6 times cloacal body diameter in males and elongated in females, about 9 times anal body diameter in length. Perspiria brevicaudata sp. nov. is characterized by having four cephalic setae and four cervical setae; small buccal cavity with dorsal tooth and minute ventral tooth; amphidial fovea unispiral, looking like double circle in outline, surrounded partially by cuticle striations; spicules arcuate with ventral velum, handle-like proximally and tapered distally; gubernaculum plate-shaped, without apophysis; twelve winged precloacal supplements present. Updated identification keys for group of Leptolaimus species characterized by the presence of both alveolar and tubular precloacal supplements and for species of Perspiria are also given.

A new free-living nematode species, Terschellingia didistalamphida sp. nov. (Nematoda: Linhomoeidae), with female intersexuality from West Bengal, India

A new species of free-living soil nematode, Terschellingia didistalamphida sp. nov., is described from paddy field in West Bengal, India. It is characterized by moderate body length (L=1.0–3.5 mm), possesses two amphids, only four cephalic setae. Amphideal fovea distant from the anterior end, stoma small and narrow, pharynx with well-developed terminal bulb. Females with amphidelphic ovaries. Males with paired testes, ventrally arcuate, short and stout spicules, gubernaculum with clearly developed dorso-caudal apophysis. Tail long and filiform, similar in both sexes. Fourteen female intersexes of Terschellingia didistalamphida sp. nov., with a prominent female reproductive structure and a less conspicuous male reproductive system, were found. These female intersexes are with well-developed vulva and prominent spicules, however, lack apophysis. A checklist for known cases of intersex across various nematode orders has been appended.

Two new species, Parabathylaimus gracilis sp. nov. and Belbolla sinica sp. nov. (Nematoda: Enoplida), from Yangma Island of the Yellow Sea, China

Two new species Parabathylaimus gracilis sp. nov. and Belbolla sinica sp. nov. are described from Yangma Island, Yellow Sea. Parabathylaimus gracilis sp. nov. is characterized by six outer labial setae three-jointed, inner labial setae and cephalic setae unjointed, amphidial fovea unispiral with circular aperture and positioned at middle of buccal cavity, spicules paired and slightly curved, gubernaculum kidney-like and distal end heavily cuticularized with a pointed projection, tail conical without long subterminal setae. Belbolla sinica sp. nov. is characterized by short body length, posterior pharynx region with seven bulbs, spicules straight with proximal and distal end tapered and middle part thickened, gubernaculum short without apophysis, two small wing-shaped precloacal supplements well developed, tail conico-cylindrical with cylindrical portion short.

One new species of Comesoma Bastian, 1865 (Nematoda: Araeolaimida: Comesomatidae) and redescription with molecular characterisation of Sphaerolaimus callisto Zograf, Pavlyuk, Trebukhova & Nguyen, 2020 (Nematoda: Monhysterida: Sphaerolaimidae) from the South China Sea

Summary One new Comesoma Bastian, 1865 species and one known Sphaerolaimus species are described from the intertidal areas of a sand beach and mangrove wetland, respectively, in Beihai City, P.R. China (South China Sea) using morphological and molecular data. Comesoma sinica n. sp. is characterised by body length 2366-2925 μm, long cephalic setae 24-32 μm, cuticle without lateral differentiation, spiral amphids with 2.5 turns, bent spicules and 3.5-4.3 cloacal body diam. long, gubernaculum parallel with spicules, and males with 20 minute precloacal supplements in the form of small pores. Molecular analyses of 18S rDNA and 28S rDNA indicate that Comesoma sinica n. sp. is closely related to other Comesomatidae genera. Sphaerolaimus callisto Zograf, Pavlyuk, Trebukhova & Nguyen, 2020, which was originally described from an estuary of northern Vietnam, the South China Sea, is characterised by long spicules and vulva situated far posterior to mid-body (82% of body length from anterior extremity), and is recorded from mangrove wetlands in Beihai City. In addition, as Sphaerolaimus longispiculatus Yang, Liu & Guo, 2021 is highly similar to S. callisto in morphology, these two species should be synonymised. Phylogenetic analyses of 18S rDNA show that S. callisto is closely related to other species of Sphaerolaimus.

Two New Species of Free-Living Marine Nematode of the Genus Anticyathus Cobb, 1920 (Linhomoeidae) from Mangroves Sediment of Shenzhen and Shantou, China

Two new species belonging to the genus Anticyathus were discovered during an ecological investigation of mangrove sediment in China. Anticyathus shenzhensis sp. nov. and Anticyathus communis sp. nov. are both characterized by: annulated cuticles; ten cephalic setae in a circle; buccal cavity lined with six longitudinal reinforcements; amphids in broken circles or cryptic spirals, located at the very anterior of the head; pharynx with anterior cuticularized, gradually enlarging in posterior portion but without bulb; conical tail; arcuate spicules, the distal ends pointed, gradually broadening towards the proximal; gubernaculum has a dorsal–caudal apophysis; female with two opposed, outstretched ovaries. Anticyathus shenzhensis sp. nov. can be distinguished by ten cephalic setae of length about 2–4 µm; amphids diameter about 20–29% of corresponding body diameter; pharynx occupy 0.07–0.10 times of body length; cardia length about 25 µm; tail length 2.5–3.4 times of anal body diameter (abd) in males and 3.4–4.7 abd in females; spicules length 51–59 µm as arc and 0.71–1.04 abd; apophysis length 18–19 µm; female vulva at 52–56% of body length. Anticyathus communis sp. nov. is identified by ten cephalic setae length about 3–5 µm; amphids diameter about 20–32% of corresponding body diameter; cardia 17–27 µm long; tail length 3.6–4.5 abd in male, 5.3–5.5 abd in female; spicules proximal with distinctly cephalated, 0.74–0.96 abd; gubernaculum shape of “L”, consisting of sleeves around spicule and dorsal–caudal apophysis; five to seven pre-anal and seven to ten post-anal almost invisible papilla or papillae-like setae occur on each ventrally submedian line on the posterior body part of male; the tip of male tail with three slight elevation; female vulva at 52% of body length. A dichotomous key for the genus Anticyathus is given and 39 sequences of 18S rRNA gene from ten individuals of Anticyathus shenzhensis sp. nov. are provided in Genbank database.

Three new species of free-living marine nematodes from the central basin of the South China Sea

ABSTRACT Three new species of free-living nematodes were discovered in the central basin of the South China Sea and are described here as Elzalia longicaudata sp. nov., Minolaimus distalamphidus sp. nov. and Setoplectus minor sp. nov. Elzalia longicaudata sp. nov. is characterised by a longer tail and longer buccal cavity relative to other members of the genus; presence of a circle of four cervical setae; spicules slender and long, which curve as the body bends; and simple gubernaculum with only one section of dorsal apophysis. Minolaimus distalamphidus sp. nov. can be distinguished from congeners by the male having lateral differentiation with six longitudinal rows of large dots; multispiral amphideal fovea with 8.5 turns; pharynx cylindrical without bulb; spicules slightly arcuate; gubernaculum rod-like without apophysis; about 17 sucker-shaped precloacal supplements; and tail conical with long filiform posterior portion. Setoplectus minor sp. nov. differs from its congeners by small body size, anterior third of pharyngeal region attenuated; cephalic setae 2 µm long; amphidial aperture circular or oval; tail elongated conical; male with a single papilliform precloacal supplement. Updated identification keys for species of the three genera are also given. http://www.zoobank.org/urn:lsid:zoobank.org:pub:623BC44A-A07F-420E-AA41-271CF85F64C6

Onyx disparamphis sp. n. (Nematoda, Desmodorida) from South Korea with a taxonomic review of the genus.

A new free-living marine nematode Onyx disparamphis sp. n. (Nematoda, Desmodorida) is described from sandy littoral of Jeju Island, South Korea. The new species differs from all other Onyx species by the unusual amphideal fovea morphology in males (elongated loop). O. disparamphis relates to O. balochinensis, and O. brevispiculatum by having simple non-double terminal pharyngeal bulb and relatively small and straight, non-sigmoid supplementary organs, but differs from them by smaller body length, shorter cephalic setae, smaller terminal pharyngeal bulb, smaller spicules, number of supplementary organs and tail shape expressed as ratio tail length/anal diameter. The genus Onyx is revised with updated genus diagnosis, and an annotated list of 23 valid species is presented. Onyx ferox is considered species inquirenda because the species is known only from a sole immature female specimen, while within Onyx, the males provide the most important distinguishing characters such as enlarged and complicated amphids, supplementary organs and copulatory spicules. For species identification, a pictorial key consisting of illustrations of simplified icons of male heads and posterior body sections, as well as a table of the most important morphometric and numerical characters are provided. Geographical distribution and habitat specifity of Onyx species is analysed briefly.

A New Species of Free-living Marine Nematode (Ptycholaimellus: Chromadoridae: Chromadorida: Nematoda) from Mangrove Wetlands in China.

This study presents a new species of free-living marine nematode, Ptycholaimellus luoyang sp. nov., from mangrove wetlands in China. The identification was confirmed by analyzing morphological characteristics and three genes: COI, 18S rDNA, and 28S rDNA. This species is distinguished from allied species by its short cephalic setae, cylindrical pharynx with anterior swelling, sclerotized transverse ridges occurring near the dorsal tooth, rod-like gubernaculum and proximal, arch-like, slightly waved, middle curved, and distally pointed spicules. The Bayesian topology was regarded as morphological evidence of P. luoyang sp. nov. being a distinct species. Interspecific and intrageneric thresholds of the K2P distance divergence have been presented here for the first time.

Three new species of Mesacanthion Filipjev, 1927 (Nematoda: Thoracostomopsidae) from Argentine coasts

Three new species of Mesacanthion Filipjev, 1927 were found along Patagonian coasts (Argentina). Mesacanthion bifidum sp. nov. is characterized by short labial and cephalic setae, onchia of equal size, spicule arcuate, and gubernaculum with caudal apophysis, ending in two teeth. The species is related to M. virile (Ditlevsen, 1930) De Coninck & Schuurmans Stekhoven, 1933. However, the spicules and gubernaculum of both species are different in shape. Mesacanthion longigubernaculum sp. nov. is characterized by its long and slender body, striated cuticle, relatively long cephalic and cervical setae, onchia of different sizes, amphidial fovea lentil-shaped, spicule arcuate, gubernaculum surrounding the spicule, and tail conical-cylindrical with terminal setae. Mesacanthion sanantoniensis sp. nov. is characterized by its long and stout body, striated cuticle, long cephalic setae, onchia of different sizes, amphidial fovea pouch-shaped, spicule arcuate, gubernaculum with dorsal apophysis, and tail conical without terminal setae. Following the key of Jeong et al. (2019), the last two species are related to M. pali Wieser, 1959 and M. longissimesetosum Wieser, 1953, so we provide a key to differentiate the four species.

Oncholaimus tripapillatus sp. nov., a New Free-Living Marine Nematode of the Genus Oncholaimus Dujardin, 1845 (Nematoda: Enoplida: Oncholaimidae) from the Subtidal Sediment of Dokdo Island, East Sea, Korea, with a New Record of O. qingdaoensis Zhang & Platt, 1983

During a survey of the free-living marine nematodes of Korea, two species belonging to the genus Oncholaimus Dujardin, 1845 were discovered. A new species, Oncholaimus tripapillatus sp. nov. and a newly recorded species, Oncholaimus qingdaoensis Zhang & Platt, 1983, are reported. Oncholaimus tripapillatus sp. nov. was collected from the washing of subtidal coarse sediments around Dokdo Island of the East Sea, Korea. Oncholaimus tripapillatus sp. nov. is characterized by a relatively long (4071–4435 µm in males and 4514–4661 µm in females) and slender body, a slightly constricted head region, relatively long cephalic setae (10–12 µm), males having a precloacal sexual protuberance bearing two small cone-shaped supplementary spines, five pairs of long cloacal setae (three pairs of precloacal and two pairs of postcloacal setae in subventral position), and three remarkable papillae near the end of the tail, with two pairs of subventral setae. The Korean specimens of Oncholaimus qingdaoensis Zhang & Platt, 1983 are almost identical to the Chinese specimens of the original description from the intertidal sand of Qingdao, China. However, the Korean specimens differ from the Chinese specimens in the longer body length in males (3379–3715 µm vs. 2380–2640 µm), the larger spicule length (47–52 µm vs. 34–36 µm), and the presence of ventral tail papillae situated around 14–16 µm from the tail tip. Detailed morphological features and illustrations of two Oncholaimus species from Korea were obtained by differential interference contrast microscopy and scanning electron microscopy. A pictorial key to the species group with distinct tail papillae among the genus Oncholaimus is also provided.