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A new species of the genus Labronema, collected in a natural mountain habitat of the southern Iberian Peninsula, in Spain, is studied, including its morphological and morphometric characterization, SEM observations, and D2-D3 28S-rRNA sequences. Labronema montanum sp. n. is distinguishable by its 1.56 to 2.08 mm long body, with lip region being offset by constriction and 19 to 24 µm broad, odontostyle 21 to 29 µm long, neck 417 to 551 µm long, pharyngeal expansion 205 to 272 µm long, the presence of three cardiac lobes at the pharyngo-intestinal junction, a long and tripartite uterus, longitudinal vulva (V = 57-60), a short and rounded caudal region (19–35 µm, c = 56-86, c = 0.5-0.8), spicules 65 to 76 µm long, and 20 to 25 nearly contiguous ventromedian supplements with hiatus.

A new species of the genus Metaxonchium is described from a natural habitat in Iran. Metaxonchium magnum sp. n. is characterized by its 3.62–4.65 mm long body, lip region cap-like and offset by constriction and 13–16 μm wide, odontostyle fusiform and 14–17 μm long, neck 1016–1359 μm long, both parts of the pharynx separated by a short isthmus-like narrowing, pharyngeal expansion occupying 74.2 (73–77)% of total neck length in females and 70.4 (66–72)% in males, female genital system mono-opistho-ovarian, didelphic, anterior genital branch a large uterine sac with a small terminal mass occupying 7–14% of body length, posterior uterus long and tripartite with a Z-like differentiation, V = 50–52, caudal region short and rounded (24–41 μm, c = 99–161, c′ = 0.5–0.7), spicules 90–105 μm long and 10–13 spaced ventromedian supplements with hiatus. Analysis of D2–D3 28S rDNA sequences of the new species suggests that Metaxonchium might not be a monophyletic taxon, a matter that should be confirmed after future research. [ABSTRACT FROM AUTHOR]

The type species of the genus Epacrolaimus, Epacrolaimus declinatoaculeatus, is studied from the re-examination of type material of Aporcelaimus vorax, its junior synonym, and the observation of several Iberian populations and a few Iranian specimens. Morphologically, it displays a recognizable morphological pattern characterized by, among other features, the incurved nature of its odontostyle aperture, presence of perioral liplets or lobes, lip region 24–31 μm wide, odontostyle 21–25 μm long and comparatively anterior location of S2N pharyngeal gland nuclei. Nevertheless, variations in some morphological traits (vagina shape and tail shape) and in several morphometrics (body length, uterus length, vulva position, tail length and spicule length) are also noted. Sequences of D2–D3 domains of the 28S rDNA, 18S rDNA and COI mtDNA were obtained from several Iberian populations. Their analyses, in particular those from D2–D3 sequences, revealed the existence of a highly supported clade ((Epacrolaimus + Sectonema) + Metaporcelaimus), with a closer relationship between Epacrolaimus and Palaearctic populations of Sectonema, whereas the remaining aporcelaimid genera occupied placements in other clades. These results are discussed, with especial emphasis on the intricate separation of Epacrolaimus and Sectonema, which display significantly different protruding stomatal structure in spite of their close evolutionary relationship as derived from molecular trees. [ABSTRACT FROM AUTHOR]

A new species of dorylaimid nematode, Aporcelinus abeokutaensis sp. n., collected from a watermelon field in Nigeria, is described, illustrated and molecularly (D2–D3 28S ribosomal DNA) studied. It is characterized by its 1.18–1.52-mm-long body, lip region offset by weak constriction, 15.5–17.5 μm broad with perioral liplets, odontostyle 18–21.5 μm long at its dorsal side or 1.1–1.3 times the lip region diameter, neck 333–401 μm long, pharyngeal expansion occupying 45–51% of total neck length, uterus simple and 0.7–1.5 times the corresponding body diameter long, V = 48–53, tail conical with finely rounded tip (33–52 μm long, c = 26–41, c′ = 1.3–1.9) and a variably distinct dorsal concavity, and male unknown. Molecular analysis reveals that the new species grouped with other species of Aporcelinus in a highly supported clade, confirming the monophyly of the genus. [ABSTRACT FROM AUTHOR]

A new species of the genus Talanema, recovered from the northwest of Iran, was described based on morphological, morphometric, and molecular data. Talanema eshtiaghii sp. n. was characterized by its 1.45–1.68 mm long body, lip region offset by constriction and 13–15 μm wide, odontostyle 15–18 μm long, double guiding ring, neck 312–362 μm long, pharyngeal expansion occupying 41–43% of the total neck length, uterus tripartite, and 111–189 μm long or 2.1–3.2 body diameters, vulva transverse (V = 55–58), tail similar in both sexes, conical with a dorsal concavity (30–44 μm, c = 33–56, c’ = 1.0–1.6), spicules 49–56 μm long, and 14–18 shortly spaced ventromedian supplements in front of the level of the anterior end of spicules, with distinct hiatus. It was compared to four closely similar species, with emphasis on the most relevant traits to distinguish them. Molecular phylogenetic studies using partial sequence of the 28S rDNA (D2–D3 segment) revealed that the new species forms a clade with other currently sequenced representatives of Talanema, tentatively supporting the monophyly of this genus.

A new species of the genus Aporcella collected from a watermelon field in Nigeria is described, including its morphological and molecular (small subunit (SSU) and large subunit (LSU) ribosomal DNA (rDNA)) characterization. Aporcella femina sp. n. is distinguished by its 3.21–3.64 mm-long body, inner cuticle layer with fine but distinct transverse striation, lip region offset by deep constriction, 22–25 μm broad, odontostyle 20–26 μm, neck 661–811 μm long, pharyngeal expansion occupying 52–56% of the total neck length, female genital system didelphic–amphidelphic, uterus 191–350 μm or 1.9–3.3 mid-body diameters long, V = 52–57, tail short and convex conoid (35–48 μm, c = 72–98, c′ = 0.7–0.9) and males absent. Phylogenetic analyses based on the partial sequence of SSU and LSU (D2–D3) rDNA revealed a close relationship of A. femina sp. n. with other Aporcella species, confirming the monophyly of the genus as well as its association to a clade made of several taxa characterized by the absence of pars refringens vaginae. [ABSTRACT FROM AUTHOR]

The new species Lenonchium zanjanense sp. n. is described from a natural habitat of Zanjan province, Iran, including line, light microscopy and scanning electron microscopy illustrations and a molecular (18S, 28S) study. It is characterized by its 3.50–4.51 mm long body, rounded lip region, continuous and 13.5–15.5 µm broad, odontostyle 21–24 µm long, neck 362–490 µm long, double guiding ring, pharyngeal expansion 190–285 µm long, female genital system didelphic–amphidelphic, uterus simple and 185–320 µm long or 3.4–5.9 times the corresponding body diameter, vulva nearly equatorial (V = 45–53), tail conical-elongated to filiform (90–165 µm, c = 23–43, c ′ = 2.4–5.3) with three or four mucro-like projections at the tip, spicules 58–64 µm long and 16–21 contiguous ventromedian supplements ending at the level of the anterior end of the spicules. The taxonomy of the genus is updated, with an emended diagnosis, list of species, key to their identification and a compendium of their main morphometrics. Lenonchium asterocaudatum is regarded as identical and a junior synonym of L. denticaudatum. New insights into the phylogeny of the group are also provided, and the classification of Lenonchium within Nordiidae is seriously questioned. [ABSTRACT FROM AUTHOR]

Two new species of the genus Aporcelinus from the USA are described and illustrated. Aporcelinus floridensis sp. n. is characterized by its 1.12–1.52 mm long body, lip region offset by marked constriction and 14.5–17.0 μm broad with perioral liplets, odontostyle 16.5–20.0 μm at its ventral side and 1.1–1.2 times the lip region diameter, neck 316–395 μm long, pharyngeal expansion occupying 43–48% of total neck length, uterus simple and 33–56 μm long or 0.8–1.2 times the corresponding body diameter, V = 48–54, female tail conical (36–49 μm long, c = 27–41, c' = 1.2–2.0) with finely rounded terminus and no hyaline portion, and male absent. Aporcelinus paolae sp. n. is characterized by its 1.29–1.80 mm long body, lip region offset by marked constriction and 14–16 μm broad, odontostyle 15–17 μm at its ventral side and 1.0–1.1 times the lip region diameter, neck 314–397 μm long, pharyngeal expansion occupying 43–53% of total neck length, uterus tripartite and 128–164 μm long or 2.6–3.6 times the corresponding body diameter, V = 53–57, female tail conical (30–39 μm long, c = 40–51, c' = 1.1–1.3) with finely rounded terminus and variably re-curved dorsad, male tail conical (27–36 μm, c = 39–59, c' = 0.9–1.2), ventrally straight and dorsally convex, spicules 48–54 μm long, and 7–9 irregularly spaced ventromedian supplements lacking hiatus. The analyses of the D2-D3 expansion segments of 28S rRNA (LSU) gene sequences of the two new species confirmed the monophyly of the genus, based upon currently available data, showing a close relationship between the genera Aporcelinus and Makatinus , and justified the placement of Aporcelaimellus , Makatinus and Aporcelinus under the subfamily Aporcelaimellinae. [ABSTRACT FROM AUTHOR]

The new species Metaxonchium toroense n. sp. from natural habitats of Costa Rica is described, including light microscopy (LM), scanning electron microscopy (SEM) and molecular (D2–D3 28S rDNA) analyses. The new species is characterized by its general size, the dimensions and appearance of its lip region, the length of the odontostyle and its fusiform aspect, the length of the neck and its pharyngeal expansion, the reduction of the anterior genital branch to a very short uterine sac without any rudiment of ovary or oviduct, tripartite and non-echinophor posterior uterus, the somewhat posterior vulva position, the length and shape of the caudal region, and the absence of males. Molecular analyses, the first to be performed on a Metaxonchium species, show a close relationship of the new species with representatives of the genera Axonchoides and Syncheilaxonchium. [ABSTRACT FROM AUTHOR]

A new species belonging to the genus Belondira is described from natural areas in Iran. Belondira coomansi n. sp. is characterized by its general size, the dimensions and appearance of its lip region, presence of distinct labial and post-labial sclerotization, the length of the odontostyle and its inconspicuous lumen and aperture, the length of the neck and its pharyngeal expansion, the reduction of the female anterior genital branch to a simple uterine sac, a very short posterior uterus, the anterior position of the vulva, the length and shape of the caudal region with distinctly thick cuticle at its tip, the length of the spicules, and the presence of only one pair of ventromedian supplements. The new species is close to Belondira brevibulba, B. sacchari , B. tenuidens and B. thornei , and it is compared to them. Molecular characterization (D2–D3 expansion segments of the rRNA large subunit) of the new species is also provided, representing only the second species of this genus for which any DNA sequence data are available. [ABSTRACT FROM AUTHOR]

A new genus and new species, Tarantobelus arachnicida, was found in the oral opening of tarantula spiders bred in captivity in Poland. The new species is characterized by having a small body (0.77–0.95 mm long in females and 0.66–0.84 mm in males), cuticle poorly annulated by transverse incisures, lateral field inconspicuous, lips separated with small cuticular flaps topping each lip, stoma panagrolaimoid with gymnostom well developed with robust and refringent rhabdia, pharynx panagrolaimoid with isthmus slightly longer than the basal bulb, intestine with cardiac (anterior) and rectal (posterior) areas with narrower walls. Mature females with intestinal cells including needle crystal packs, excretory pore at isthmus level, female reproductive system panagrolaimoid with post-vulval sac 0.4–0.8 times the length of the corresponding body diameter and having very thick walls, vulva very prominent, female rectum 0.8–1.3 times the length of the anal body diameter, female tail conical with acute tip with phasmids at 58–62% of its length. Male tail conical with long and thin mucro, spicules ventrad bent having rounded manubrium and thick gubernaculum. Description, measurements and illustrations of the new species are provided. Molecular analyses show its relationship with Brevibucca and Cuticonema. On the other hand, Medibulla and its corresponding subfamily Medibullinae, previously in Osstellidae, are transferred to Panagrolaimidae, being Shahnematinae, the junior synonym of Medibullinae. Indocephalobus, recently proposed and located in the family Panagrolaimidae, is considered a junior synonym of Diplogastrellus (Diplogasteromorpha), and its only species, I. zebrae, is considered a junior synonym of D. gracilis. In addition, a key to identification of panagrolaimoid genera is included. [ABSTRACT FROM AUTHOR]

A new species of the genus Oscheius, O. saproxylicus sp. n., collected in decaying wood obtained from an orchard in Southern Iberian Peninsula, is reported. A detailed description, including morphometrics, LM and SEM images, and molecular (18S and 28S rDNA genes) information is provided. The female is characterized by a moderately long body, lateral field with three longitudinal ridges, midbody vulva, and conical tail with acute tip. It was distinguished from its closest relative, O. dolichura, by a shorter tail and longer rectum. The male was not found. Morphological and molecular data support its belonging to Dolichura-group. Molecular analyses show that both Insectivorus and Dolichura groups are related to each other, being proposed as subgenera of the genus Oscheius as Oscheius and Dolichorhabditis. Finally, an updated taxonomy of the genus is presented, with generic and subgeneric diagnoses, list of species and a key to their identification.

Two new species of the genus Crassolabium are described from natural areas in Vietnam. Crassolabium aenigmaticum sp. nov. is characterized by its body 1.23-1.58 mm long, lip region continuous, odontostyle 17.0-19.0 μm long, neck 320.0-397.0 μm long, uterus tripartite, pars refringens vaginae with two triangular pieces separated by an intermediate sclerotized area, V = 54-59, vulva longitudinal, tail short and rounded in both sexes, spicules 43.0-48.0 μm long, and seven to eight spaced ventromedian supplements. C. vietnamense sp. nov. can be distinguished in having body 1.55-1.88 mm long, lip region offset by constriction, odontostyle 19.5-22.0 μm long, neck 370.0-448.0 μm long, uterus very long and tripartite, pars refringens vaginae with two close together pieces, V = 55-59, vulva transverse and usually covered with a plug, tail short and rounded in both sexes, spicules 53.0-55.0 μm long, and eight to nine spaced ventromedian supplements, two of them within the range of spicules. [ABSTRACT FROM AUTHOR]

A new Iranian population of Lindseyus costatus is characterized, including morphometrics, microphotographs, and molecular (18S, 28S rDNA) studies. It is compared with previously known populations. The results derived from molecular analyses failed to find close evolutionary relationships with other traditional genera of Belondiridae and Swangeriinae, adding more uncertainties about the internal phylogeny of the family. The taxonomy of Lindseyus is revised, with a new diagnosis, list of species, key to their identification, and a compilation of their main morphometrics.

Free-living aquatic nematodes are abundant, diverse and of general environmental importance. However, knowledge of species distributions of both marine and freshwater nematodes is sparse. Species distribution data are crucial for evaluating environmental impacts from human activities and to conduct integrated nematode community assessments. Basic knowledge on taxonomy and species descriptions is lacking for many regions due to decreasing taxonomic expertise, yet it is essential for biodiversity research and for building molecular sequence libraries for the application of methods such as environmental DNA. In order to encourage and facilitate taxonomic and descriptive work on this understudied group, we present here a framework for nematode species description. We begin by providing a brief overview of nematology history, then provide suggestions of microscopic methods that should be used and provide a list of characters essential for morphometric species descriptions. Finally, we briefly discuss common molecular sequencing approaches that are commonly used in nematode taxonomic literature.

Background: The genus Enchodelus is an intriguing free-living dorylaimid nematode taxon. Its representatives display a distinct distributional pattern as they are mainly spread in high altitudinal enclaves of the Northern Hemisphere, being often associated with mosses and cliff vegetation. Although their feeding habits have not been studied with experimental protocols, it is traditionally assumed that they are omnivorous.The genus Enchodelus has not been recently revised; descriptions of many 'old species' (that have been described long ago and have not been reported since their original discovery) are of poor quality, hardly discoverable and do not conform to the nowadays taxonomical standards. Thus, a comprehensive compilation and analysis of their literature data is indispensable to provide new insights into the taxonomy of the genus and to elucidate its evolutionary relationships., New Information: This contribution provides a cyber catalogue of all Enchodelus species, 28 in total. It compiles available information from the key European Research Infrastructures, such as TreatmentBank, Swiss Institute of Bioinformatics Literature Services (SIBiLS), the Catalogue of Life (CoL), Global Biodiversity Information Facility (GBIF), European Nucleotide Archive (ENA) and Biodiversity Literature Repository (BLR). Data about their distribution (geographical records and habitats) are incorporated too and all brought together. It is completed with discussion and notes for some species, along with information on species distributions and microhabitats. Here, all available information on Enchodelus species is brought together. This will contribute to a more complete assessment of species diversity and distribution and support further biogeographical and ecological research.Besides, type material Enchodelusvestibulifer Altherr, 1952, deposited in the Museo Cantonale di Storia Naturale di Lugano (Switzerland), is re-examined and the species is considered as incertae sedis . Further, a new species of the genus found in Caucasus, Georgia is described after its morphological and molecular study; also morphological and molecular data for E.macrodorus (de Man, 1880) Thorne, 1939, the type species of the genus, collected from Spain are provided., (Milka Elshishka, Aleksandar Mladenov, Stela Altash, Sergio Álvarez-Ortega, Reyes Peña-Santiago, Vlada Peneva.)

Two new species of the genus Sectonema found in northern Iran are characterized, including morphological descriptions and molecular (18S-, 28S-rDNA) analyses. Sectonema tehranense sp. nov. is distinguished by its 7.22 - 8.53 mm long body, lip region offset by constriction and 24 - 31 μm wide with perioral lobes and abundant setae- or cilia-like projections covering the oral field, mural tooth 15.5 - 17 μm long at its ventral side, neck 1091 - 1478 μm long, pharyngeal expansion occupying 61 - 71% of the total neck length, female genital system diovarian, uterus simple and 3.9 - 4.2 times the corresponding body diameter long, transverse vulva ( V = 49 - 59), tail short and rounded (44 - 65 μm, c = 99 - 162, c' = 0.6 - 0.8), spicules 111 - 127 μm long, and 7 - 10 spaced ventromedian supplements with hiatus. Sectonema noshahrense sp. nov. displays a 4.07 - 4.73 mm long body, lip region offset by constriction and 23 - 25 μm wide with perioral lobes and abundant setae- or cilia-like projections covering the oral field, odontostyle 14 - 14.5 μm long, neck 722 - 822 μm long, pharyngeal expansion occupying 66 - 68% of the total neck length, female genital system diovarian, uterus simple and 2.4 - 2.7 times the corresponding body diameter long, transverse vulva ( V = 54 - 55), tail convex conoid (39 - 47 μm, c = 91 - 111, c' = 0.8 - 0.9), spicules 82 μm long, and seven spaced ventromedian supplements with hiatus. Molecular analyses confirm a maximally supported ( Epacrolaimus + Metaporcelaimus + Sectonema ) clade and a tentative biogeographical pattern, with sequences of Indolamayan taxa forming a clade separated from those of Palearctic ones. Parallel or convergent evolution processes might be involved in the phylogeny of the species currently classified under Sectonema. This genus is certainly more heterogeneous than previously assumed.

A new species of the free-living nematode genus Trachactinolaimus , collected in natural habitats of northern Iran, is described, including morphological and molecular (28S-rDNA) data. Trachactinolaimus persicus sp. n. is characterized by its 1.95-2.44 mm long body, lip region weakly offset by depression and 18-20 μm wide, odontostyle 25-27 μm long, neck 540-636 μm long, pharyngeal expansion occupying one-half of the total neck length, bipartite uterus 2.6-3.9 body diameters long, vulva ( V = 49-53) pore-like, tail long and filiform in both sexes (174-223 μm, c = 10.0-13.4, c' = 5.9-7.0 in females, 165-196 μm, c = 10.7-13.8, c' = 4.6-5.8 in males), spicules 68-75 μm long, and 12-14 almost contiguous ventromedian supplements with hiatus. Molecular data supports the monophyly of the genus and the hypothesis that Dorylaimidae are the sister group of actinolaims. The taxonomy of Trachactinolaimus is updated, including diagnosis, list of species, key to their identification, and a compendium of their main morphometrics. Dominiactinolaimus is regarded as its junior synonym.

A new species of the genus Aporcella, collected in replanted coffee orchards in Central Highland of Vietnam, is described and illustrated. Aporcella daklakensis sp. n. is characterized by its 1.63-1.98 mm long body, lip region offset by weak constriction and 14-15 μm broad, odontostyle 13-15 μm long or equal to lip region diameter, neck 400-565 μm long, pharyngeal expansion 205-335 μm long and occupying 51-60% of the total neck length, female genital system diovarian with very poorly developed genital tract and transverse vulva (V = 53-59), tail conical with rounded terminus (31-39 µm, c = 43-57, c' = 1.0-1.4), visibly subdigitate and bearing cuticular irregularities at its ventral side, and male absent. The new species is compared with its closest Aporcella representatives.

The evolutionary relationships of the nematode genus Loofilaimus are explored with an integrative approach, combining morphological and molecular (28S-rDNA) data. Never recorded since its original description in 1998, the finding of fresh specimens of its type and only species, L. phialistoma , allowed us to obtain SEM observations and sequencing, both for the first time, resulting in relevant aspects to elucidate its phylogeny. Morphologically, the genus is characterized by two autapomorphies affecting its lip region and pharynx. Molecular study revealed that it represents a very restricted evolutionary trend within Dorylaimida. The clade (Nygolaimina + ( Loofilaimus + Dorylaimina)) is well supported. Loofilaimidae is accepted as a separate and valid family, which should also include Bertzuckermania.

Crassolabium unicum sp. n., collected from a natural habitat in Vietnam, is described and illustrated. The new species is characterized by its 0.770.94 mm long body, three-layered cuticle, lip region offset by depression and 1213.5 µm broad, odontostyle 13.515 µm long with wide aperture occupying 3646% of its length, neck 235260 µm long, pharyngeal expansion 117131 µm long or occupying 4752% of total neck length, anterior part of intestine presenting very distinct folds, female genital system didelphic-amphidelphic, uterus simple and 2843 µm or 0.70.9 body diameters, vulva transverse (V = 4552), prerectum bearing a blind postrectal sac, caudal region short and rounded (2125 µm, c = 4561, c' = 0.60.8) with two (dorsal and ventral) lacunae between outer and intermediate cuticle layers, and male unknown. It is compared with the similar representatives of the genus.

Three Iranian populations of Discolaimium dubium are studied, including their morphological and morphometric characterization, molecular analysis (LSU-rDNA) and the description of the male for the first time. For comparative purposes, this species is distinguished by its 1.10 to 1.40 mm long body, lip region offset by constriction and 8 to 10 µm wide, odontostyle 7.5 to 10.5 µm long with aperture occupying 59 to 76% of total length, neck 300 to 362 µm, pharyngeal expansion 127 to 181 µm long or 44 to 46% of the total neck length, uterus simple and 38 to 53 µm or 1.2 to 1.5 times the body diameter long, V  = 52 to 58, tail conical (32-38 µm, c  = 32-43, c'  = 1.6-2.0) with rounded tip and a hyaline portion occupying 14 to 15% of tail length, spicules 30 to 32 µm long, and two or three widely space ventromedian supplements with hiatus. Both morphological and molecular data support its belonging to the genus Aporcella , whose monophyly is confirmed and to which the species is formally transferred as A. dubia (Das et al., 1969) comb. n., (© 2021 Authors.)

Epidorylaimus procerus sp. n., collected from a natural habitat in Vietnam, is described and illustrated. It is distinguishable by its 2.16 to 2.46-mm-long body, lip region offset by depression and 15 to 17-µm broad, odontostyle 32 to 35-µm long, neck 415 to 461-µm long, pharyngeal expansion occupying 47 to 52% of the total neck length, uterus 76 to 130-µm long or 1.0 to 1.5-body diameters, vulva transverse ( V  = 40-43), caudal region conical elongate (157-186 µm, c  =12.1-14.4, c'  = 4.4-5.5) with blister-like bodies, and hyaline portion occupying one-fourth its length, and males absent. Molecular analysis shows a close relationship of the new species and E. lugdunensis , supporting monophyly of the genus Epidorylaimus ., (© 2020 Authors.)

Two species of the genus Aporcella, one new and one previously known, collected from cultivated fields in Iran are studied. Description, morphometrics, illustrations (both line and microphotographs) and D2-D3 sequences are provided for Aporcella talebii sp. n., which is characterized by its 1.66-2.02-mm-long body, lip region offset by constriction and 15-17 μm broad, odontostyle 14-17.5 μm long, neck 412-484 μm long, pharyngeal expansion occupying 46-50% of total neck length, uterus simple and 1.6-2.0 times the corresponding body diameter long, V = 52-59, tail conical (40-50 μm, c = 37-47, c' = 1.1-1.4) with a weak but perceptible dorsal concavity at the end and male absent. Morphometrics, microphotographs and D2-D3 sequences of Aporcella simplex are also presented, this being its first Asian record. Molecular analyses confirm the monophyly of the genus, its close relationship with other taxa lacking pars refringens vaginae and the polyphyly of Aporcelaimidae.

Two species of the genus Pungentus , one new and one known, collected in natural vegetation and cultivated soils in northwest of Iran, are studied. Pungentus sufiyanensis n. sp. is characterized by its 1.22 to 1.57 mm long body, offset lip region by a constriction and 7 to 9 μm broad, 18 to 21 μm long odontostyle, 304 to 348 μm long neck, 133 to 161 μm long esophageal expansion, mono - opisthodelphic female genital system without anterior uterine sac, slightly backward directed vagina, absence of pars refringens vaginae , V  = 47 - 54, rounded-conoid caudal region (17.5-23 μm, c  = 65-84, c ´ = 0.7-1) with saccate bodies, and the absence of male. Molecular analysis, based on D2-D3 expansion segments of the 28S rDNA (LSU), confirms the monophyly of the family Nordiidae and suggests the monophyly of the genus Pungentus , with the new species forming a clade with other Iranian species. New data are presented for six Iranian populations of P. engadinensis , and an updated key for the identification of Pungentus species is also provided., Two species of the genus Pungentus , one new and one known, collected in natural vegetation and cultivated soils in northwest of Iran, are studied. Pungentus sufiyanensis n. sp. is characterized by its 1.22 to 1.57 mm long body, offset lip region by a constriction and 7 to 9 μm broad, 18 to 21 μm long odontostyle, 304 to 348 μm long neck, 133 to 161 μm long esophageal expansion, mono - opisthodelphic female genital system without anterior uterine sac, slightly backward directed vagina, absence of pars refringens vaginae , V  = 47 − 54, rounded-conoid caudal region (17.5–23 μm, c  = 65–84, c ´ = 0.7–1) with saccate bodies, and the absence of male. Molecular analysis, based on D2-D3 expansion segments of the 28S rDNA (LSU), confirms the monophyly of the family Nordiidae and suggests the monophyly of the genus Pungentus , with the new species forming a clade with other Iranian species. New data are presented for six Iranian populations of P. engadinensis , and an updated key for the identification of Pungentus species is also provided.

The identity of Eucephalobus oxyuroides is discussed after studying two Iberian populations that fit the original description of the species. A new characterization is consequently provided as follows: 0.49 to 0.70 mm long body, lip region continuous with the adjoining body and bearing short probolae prongs, neck 132 to 158 µm long, spermatheca 23 to 47 µm long or 1.0 to 1.8 times the corresponding body diameter, post-vulval uterine sac 40 to 54 µm long or 2.0 to 2.5 times as long as the body diameter, V   =  58 to 64, female tail conical elongate with very acute terminus (60-79 µm, c  = 7.1-10.0, c ' = 4.9-5.8), male tail conical (36-49 µm, c  =10.9-14.3, c ' = 2.4-3.4) with an elongate acute mucro, and spicules 21 to 22 µm long. Previous records of the species are revised. An emended diagnosis of the genus is proposed, and its taxonomy is updated with a list of species, key to their identification and illustrations. The evolutionary relationships of Eucephalobus , as derived from the analyses of 18S and 28S rDNA fragments, reveals that it occupies a basal position within the subfamily Cephalobidae., The identity of Eucephalobus oxyuroides is discussed after studying two Iberian populations that fit the original description of the species. A new characterization is consequently provided as follows: 0.49 to 0.70 mm long body, lip region continuous with the adjoining body and bearing short probolae prongs, neck 132 to 158 µm long, spermatheca 23 to 47 µm long or 1.0 to 1.8 times the corresponding body diameter, post-vulval uterine sac 40 to 54 µm long or 2.0 to 2.5 times as long as the body diameter, V   =  58 to 64, female tail conical elongate with very acute terminus (60-79 µm, c  = 7.1-10.0, c ′ = 4.9-5.8), male tail conical (36-49 µm, c  =10.9-14.3, c ′ = 2.4-3.4) with an elongate acute mucro, and spicules 21 to 22 µm long. Previous records of the species are revised. An emended diagnosis of the genus is proposed, and its taxonomy is updated with a list of species, key to their identification and illustrations. The evolutionary relationships of Eucephalobus , as derived from the analyses of 18S and 28S rDNA fragments, reveals that it occupies a basal position within the subfamily Cephalobidae.

A new species of the genus Metarhabditis, M. giennensis sp. n., collected from a riverbank poplar forest in the southern Iberian Peninsula, is described and illustrated, including SEM observations. The new species is characterized by its 1.01-1.16 mm long body in females and 0.77-0.98 in males, cuticle with very fine transverse striation, lip region 9-14 µm broad and consisting of six swollen rounded lips fused in pairs, stoma 14-25 µm long with tubular gymno-promesostegostom, pharynx with slightly swollen metacorpus and slender isthmus, nerve ring, excretory pore and deirids located at isthmus level, female reproductive system didelphic-amphidelphic, vulva equatorial (V = 49-50), female rectum length 1.2-1.7 times the anal body width, female tail conical-elongate with acute tip (123-199 µm, c = 5.8-8.2, c' = 8.2-11.1), male tail conical (34-56 µm, c = 15.5-25.7, c' = 2.4-3.5), bursa leptoderan, 32-41 µm long spicules with rounded and ventrally bent manubrium, and 17-20 µm long gubernaculum. An updated list of species of the genus and a key for their identification are also provided. [Zoobank URL: urn:lsid:zoobank.org:act:7EBAC9DB-A148-4A1A-97E5-3B796D0839BF].

The new species Lenonchium zanjanense sp. n. is described from a natural habitat of Zanjan province, Iran, including line, light microscopy and scanning electron microscopy illustrations and a molecular (18S, 28S) study. It is characterized by its 3.50-4.51 mm long body, rounded lip region, continuous and 13.5-15.5 µm broad, odontostyle 21-24 µm long, neck 362-490 µm long, double guiding ring, pharyngeal expansion 190-285 µm long, female genital system didelphic-amphidelphic, uterus simple and 185-320 µm long or 3.4-5.9 times the corresponding body diameter, vulva nearly equatorial (V = 45-53), tail conical-elongated to filiform (90-165 µm, c = 23-43, c' = 2.4-5.3) with three or four mucro-like projections at the tip, spicules 58-64 µm long and 16-21 contiguous ventromedian supplements ending at the level of the anterior end of the spicules. The taxonomy of the genus is updated, with an emended diagnosis, list of species, key to their identification and a compendium of their main morphometrics. Lenonchium asterocaudatum is regarded as identical and a junior synonym of L. denticaudatum. New insights into the phylogeny of the group are also provided, and the classification of Lenonchium within Nordiidae is seriously questioned.

Two Metaporcelaimus species, one new and one known, are described from Ukraine. Metaporcelaimus petrophilus sp. n. is characterized by its 1.30-1.58 mm long body, lip region offset by deep constriction and 16-18 µm broad, odontostyle 15-17 µm long, neck 360-413 µm long, pharyngeal expansion occupying 47-54% of total neck length, uterus simple and 83-125 µm long or 1.6-2.7 times the corresponding body diameter, uterine eggs with granulate shell, V = 51-55%, tail conical (35-40 µm, c = 33-42, c' = 1.4-1.8 in females), spicules 43-50 µm long, and 9-13 spaced ventromedian supplements with hiatus. New data, including the first description of male specimens and SEM study, are provided for M. ovogranulosus, the Ukrainian populations of which are nearly identical to the type population from California.

A new species of the genus Tylencholaimus, collected in natural areas of Iran, is described and illustrated, including SEM observations. Tylencholaimus discus sp. n. is characterized by its 0.65-0.76 mm long body, lip region offset by weak constriction and 7-7.5 µm broad with a conspicuous perioral disc, odontostyle 6-7 µm long, odontophore 9-10.5 µm long and visibly flanged rather than knobbed, neck 230-259 µm long with anterior region weakly muscular and basal expansion 98-125 µm long or occupying 42-49% of total neck length, female genital system mono-prodelphic, posterior branch reduced to a uterine sac 2-20 µm long or much shorter (0.1-0.6 times) than body diameter but very occasionally consisting of uterus, sphincter and a small terminal mass all together measuring 35-40 µm long, V = 65-74, tail short and rounded (13-17 µm, c = 41-57, c' = 0.6-0.8), and male unknown.

Two new species of the genus Aporcelinus from the USA are described and illustrated. Aporcelinus floridensis sp. n. is characterized by its 1.12-1.52 mm long body, lip region offset by marked constriction and 14.5-17.0 μm broad with perioral liplets, odontostyle 16.5-20.0 μm at its ventral side and 1.1-1.2 times the lip region diameter, neck 316-395 μm long, pharyngeal expansion occupying 43-48% of total neck length, uterus simple and 33-56 μm long or 0.8-1.2 times the corresponding body diameter, V = 48-54, female tail conical (36-49 μm long, c = 27-41, c' = 1.2-2.0) with finely rounded terminus and no hyaline portion, and male absent. Aporcelinus paolae sp. n. is characterized by its 1.29-1.80 mm long body, lip region offset by marked constriction and 14-16 μm broad, odontostyle 15-17 μm at its ventral side and 1.0-1.1 times the lip region diameter, neck 314-397 μm long, pharyngeal expansion occupying 43-53% of total neck length, uterus tripartite and 128-164 μm long or 2.6-3.6 times the corresponding body diameter, V = 53-57, female tail conical (30-39 μm long, c = 40-51, c' = 1.1-1.3) with finely rounded terminus and variably re-curved dorsad, male tail conical (27-36 μm, c = 39-59, c' = 0.9-1.2), ventrally straight and dorsally convex, spicules 48-54 μm long, and 7-9 irregularly spaced ventromedian supplements lacking hiatus. The analyses of the D2-D3 expansion segments of 28S rRNA (LSU) gene sequences of the two new species confirmed the monophyly of the genus, based upon currently available data, showing a close relationship between the genera Aporcelinus and Makatinus, and justified the placement of Aporcelaimellus, Makatinus and Aporcelinus under the subfamily Aporcelaimellinae.

One known (M. romanicus) and two new species of the genus Metaporcelaimus, collected in natural and semi-natural habitats of Ukraine, are described and illustrated. Metaporcelaimus concinnus sp. n. is characterized by its 3.09-4.58 mm long body, lip region 16.5-19.5 µm broad and visibly wider than the adjacent body, odontostyle 17-19 µm long, neck 745-865 µm long, pharyngeal expansion occupying 62-66% of total neck length, uterus tripartite and 3.9-5.7 times the corresponding body diameter, vulva longitudinal (V = 49-53%), tail conical (44-54 µm, c = 67-94, c' = 1.0-1.3 in females), spicules 79-86 µm long with strongly bifurcate distal end, and 10-14 irregularly spaced ventromedian supplements without hiatus. Metaporcelaimus declivicaudatus sp. n. is characterized by its 2.88-3.66 mm long body, lip region 23-28 µm broad, odontostyle 24-26 µm long, neck 634-788 µm long, pharyngeal expansion occupying 48-56% of total neck length, uterus tripartite and 3.0-3.4 times the corresponding body diameter long, vulva transverse (V = 51-55%), tail conical (45-65 µm, c = 53-63, c' = 1.0-1.2) with rounded terminus, spicules 102-113 µm long, and 12-14 spaced ventromedian supplements without hiatus. New information about M. romanicus is also provided, confirming available data about this species.

A new species of the genus Aporcelinus, A. elongicaudatus sp. n., collected from natural habitats of Costa Rica, is described and illustrated. The new species is characterized by its 0.92-1.05 mm long body, lip region offset by weak constriction and 15 µm broad, odontostyle 15-18 µm or 1.0-1.2 times the lip region diameter, neck 270-300 µm long, pharyngeal expansion 130-150 µm long or 45-55% of total neck length, uterus 33-41 µm long or 0.70-0.85 times the corresponding body diameter (but certainly longer), vulva transverse (V = 49-51), and tail conical elongated (45-71 µm, c = 14-22, c' = 2.0-3.2) and dorsad bent.

Two new species of the genus Metaxonchium are described from natural habitats of Vietnam. Metaxonchium bonkowskii sp. n. is characterized by its 1.69-2.23 mm long body, lip region offset by weak constriction and 9.5-10.5 µm broad, odontostyle 11-13 µm long, neck 673-868 µm long with the pharyngeal expansion occupying 66-77% of its length, anterior genital branch reduced to a uterine sac 75-135 µm long or 4-7% of body length, posterior uterus tetrapartite and including a Z-like differentiation, V = 51-55, and female tail short and rounded (37-51 µm, c = 66-97, c' = 0.5-0.7). Metaxonchium silvaticum sp. n is characterized by its 1.28-1.43 mm long body, lip region offset by weak depression and 7.0 µm broad, odontostyle 8-9 µm long, neck 502-630 µm long with the pharyngeal expansion occupying 65-76% of its length, anterior genital branch reduced to a uterine sac 65-80 µm long or 4-6% of body length, posterior uterus tripartite, non-echinophor, V = 52-57, tail short and rounded (18-23 µm, c = 56-74, c' = 0.6-0.8) with abundant blister-like or saccate bodies, spicules 41 µm long, and seven spaced ventromedian supplements.

A new species of the genus Eudorylaimus is described from Kahaq region, Maragheh, East Azarbaijan province in Iran. Eudorylaimus kahaqensis sp. n. is characterized by its 1.40-1.75 mm long body, lip region nearly continuous and 17-21 µm wide and bearing a weakly sclerotized but distinct cephalic framework, cheilostom broad and with convex walls, odontostyle 21-23 µm long with aperture occupying 33-44% of its length, presence of a dorsal coelomocyte a short distance behind the nerve ring, neck 347-397 µm long, DN rather posterior (66-70%), pharyngeal expansion 162-205 µm or occupying 45-53% of total neck length, presence a dorsal cell mass at level of pharyngo-intestinal junction, V = 48-52, caudal region conical elongate (50-73 µm, c = 24-30, c' = 1.9-2.6 in females; 45-68 µm, c = 22-32, c' = 1.7-2.3 in males) and regularly curved ventrad with large hyaline portion, spicules 48-55 µm long and 7-9 irregularly spaced ventromedian supplements lacking hiatus.

The taxonomy and the systematics of the genus Makatinus are discussed by means of the characterization of its morphological pattern and the first molecular (D2-D3 expansion segments of 28S rDNA) analysis of a representative of this taxon, Makatinus crassiformis from Costa Rica. The presence of two or more pairs of male ad-cloacal genital papillae is the most characteristic autapomorphy of the genus, but the status of its species on this concern differ among them. Both morphological and molecular data support a relationship with Aporcelaimellus , which, however, might not be as close as usually assumed. An emended diagnosis of the genus, a key to species identification, and a compendium of their morphometrics are provided. Makatinus siddiqii is regarded as species inquirenda , Makatinus simus is retained under Eudorylaimus , and Makatinus tritici becomes a junior synonym of Aporcelaimellus tritici .

A new species of the genus Myolaimus is described from agricultural areas in the southeast of the Iberian Peninsula. Myolaimus ibericus sp. n. is characterized by its 560-783 μm long body in females and 526-731 μm in males, cuticle often appearing swollen and baggy, lateral field with one longitudinal wing, lip region with six amalgamated lips having ten (6 + 4) setiform papillae, stoma consisting of a wider anterior chamber (cheilo-gymnostom) and a tubular posterior part (stegostom) separated by a well developed dorsal tooth and two small, lateral (one right and another left) teeth, glottoid-like apparatus structure appearing at metastom, pharyngeal corpus 1.7-2.6 times the isthmus length, excretory pore and deirids located at metacorpus level, deirids pore-like in females and seta-like in males, female reproductive system monodelphic-prodelphic with antidromous ovary, post-uterine sac 1.7-2.7 times the corresponding body diameter long, V = 50-56, female rectum 1.3-2.0 times the anal body diameter long, female tail conical-elongate (54-70 μm, c = 9.9-13.1, c' = 4.4-5.8) often enveloped by the baggy cuticle, male tail conoid (8-10 μm, c = 58.4-73.1, c' = 1.1-1.4) and ventrally constricted at its middle, bursal structure with seven (4+1+2) pairs of genital papillae. This is the first record of the genus from the Iberian Peninsula. Description, measurements and illustrations, including SEM photographs are provided. An illustrated compendium of the posterior ends of males in Myolaimus species is also presented.

A new species of the genus Protorhabditis is described from agricultural areas in the South East of the Iberian Peninsula. Protorhabditis hortulana sp. n. is distinguished by its very small body length (189-222 μm in females), lateral field with two longitudinal wings, lip region rounded with fused lips, stoma 10-13 μm long lacking glottoid apparatus, pharynx with distinctly swollen metacorpus, excretory pore and deirids at basal bulb level, female reproductive system outstretched and spermatheca with self-sperm, vulva slightly postequatorial (V=54-62), female tail conoid (14-19 μm, c= 11.7-17.6, c'= 1.6-2.4) with finely rounded tip, and males unknown. Description, measurements and illustrations, including SEM photographs are provided. A compendium of species of Protorhabditis is also given and illustrated.

Sectonema caobangense sp. n. from evergreen forest soil in Vietnam is described, including scanning electron micrograph (SEM) observations and D2-D3 LSU rDNA analysis. The new species is characterized by its 3.12 to 5.80 mm long body, lip region offset by deep constriction and 21 to 23 μm broad, mural tooth 13 to 14 μm long at its ventral side, 940 to 1,112 μm long neck, pharyngeal expansion occupying 61% to 69% of total neck length, uterus a long simple tube-like structure 292 to 363 μm long or 2.7 to 2.9 times the corresponding body diameter, pars refringens vaginae well developed, V = 48 to 56, short (36-51 μm, c = 77-132, c' = 0.5-0.8) and rounded tail, 87 to 99 μm long spicules, and four or five irregularly spaced ventromedian supplements bearing hiatus. Sectonema caobangense sp. n. differs from the typical pattern of Sectonema in the nature of the stomatal protrusible structure, bearing a mural tooth attached to the ventral side of the stoma. Molecular data obtained and the derived evolutionary trees support a close phylogenetic relationship with other Sectonema species.

A new species, the third one from Vietnam, of the genus Aporcelinus is described from natural areas. Aporcelinus falcicaudatus sp. n. is characterized by its 1.28 to 1.63 mm long body, lip region offset by weak constriction and 16 to 18 µm broad, odontostyle 18 to 21 µm at its ventral side, neck 354 to 406 µm long, uterus tripartite and 61 to 95 µm long, V = 50 to 55, tail strongly recurved dorsad and conical (23-31 µm, c = 43-58, c' = 0.7-0.9) with finely rounded tip, and male absent. Scanning electron microscope (SEM) study, the first of a representative of the genus, shows a lip region pattern significantly different from that observed in the typical aporcelaimid taxa.

Two new species of Aporcelinus from Vietnamese natural habitats are studied, described and illustrated, including line drawings and light microscope (LM) pictures. Aporcelinus paramamillatus sp. n. is characterized by its 1.71-2.14 mm long body, lip region 21-22 μm broad, odontostyle 22-24 μm long at its ventral side, neck 451-503 μm long, uterus tripartite and 71-94 µm long, V = 53-54, tail conical with finely rounded tip, ending in a short peg-like terminus, occasionally slightly re-curved dorsad (24-34 μm, c = 50-77, c' = 0.6-0.9) and unknown male. Aporcelinus paraseychellensis sp. n. is distinguished by its 1.20-1.46 mm long body, lip region 16-18 μm broad, odontostyle 20 μm long at its ventral side, neck 354-368 μm long, uterus tripartite and 176-241 µm long, V = 52-54, tail conical with acute tip and hardly re-curved dorsad, spicules 62 μm long, and 12 regularly spaced ventromedian supplements lacking hiatus.

Recently, specimens of Cephalobus topali, collected from an agricultural area from northern Vietnam, are described, including SEM study. They are characterized by their its 306-347 µm long body in females, lateral field with two alae or 3-4 longitudinal incisures, lip region with three pairs of asymmetrical conoid lips, three low and rounded labial probolae separate from the corresponding pair of lips by an incisure, U-shaped primary axils without guard processes, V-shaped secondary axils without guard processes, pharyngeal corpus slightly fusiform and 2.6-3.1 times the isthmus length, spermatheca and postvulval sac poorly developed, female tail conoid (18-24 µm, c = 12.7-17.0, c' = 1.8-2.7) with rounded terminus ending in an acute or wart-shaped mucro, phasmid at 29-34% of tail length, and male unknown. SEM pictures reveal that lip region pattern significantly differs from that found in members of Cephalobus and fits that observed in Acrobeloides, so that the species is transferred to this genus. Cephalobus quadrilineatus is provisionally maintained as different from C. topali.