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Two new and two known species of the genus Paraoxydirus Jairajpuri and Ahmad, 1978 are described and illustrated from Western Ghats of India. P. vulvalpapillatus n. sp. is characterized by having large sized body (L = 4.6 – 4.8 mm); lip region continuous with completely amalgamated lips; amphidial fovea cup – shaped; 5 – 6 μm long odontostyle; 11 – 13 μm long odontophore; pharyngeal expansion about 28 – 36 % of neck length; transverse vulva; vulval papillae conspicuous; males with 46 – 54 μm long spicules; 11 – 14 continuous ventromedian supplements and long filiform tail similar in both sexes. P. indicus n. sp. is characterized by having large sized body (L = 4.0 – 4.8 mm); lip region poorly offset with amalgamated lips; amphidial fovea cup-shaped; 7 – 8 μm long, robust odontostyle; 17 – 18 μm long odontophore; pharyngeal expansion about 32 – 40 % of neck length; 21 – 26 μm long cardia; longitudinal vulva; 748 – 894 μm long filiform tail; males with 45 – 54 μm long spicules and 12 – 15 continuous ventromedian supplements. P. gigas Jairajpuri, 1964 and P. novus Jairajpuri, 1965 are redescribed based on specimens collected from several localities. A diagnostic Key and compendium to the identification of its eight valid species is provided.

Background Within the class Enoplea, the earliest-branching lineages in the phylum Nematoda, the relatively highly conserved ancestral mitochondrial architecture of Trichinellida is in stark contrast to the rapidly evolving architecture of Dorylaimida and Mermithida. To better understand the evolution of mitogenomic architecture in this lineage, we sequenced the mitogenome of a fish parasite Pseudocapillaria tomentosa (Trichinellida: Capillariidae) and compared it to all available enoplean mitogenomes. Results P. tomentosa exhibited highly reduced noncoding regions (the largest was 98 bp), and a unique base composition among the Enoplea. We attributed the latter to the inverted GC skew (0.08) in comparison to the ancestral skew in Trichinellidae (-0.43 to -0.37). Capillariidae, Trichuridae and Longidoridae (Dorylaimida) generally exhibited low negative or low positive skews (-0.1 to 0.1), whereas Mermithidae exhibited fully inverted low skews (0 to 0.05). This is indicative of inversions in the strand replication order or otherwise disrupted replication mechanism in the lineages with reduced/inverted skews. Among the Trichinellida, Trichinellidae and Trichuridae have almost perfectly conserved architecture, whereas Capillariidae exhibit multiple rearrangements of tRNA genes. In contrast, Mermithidae (Mermithida) and Longidoridae (Dorylaimida) exhibit almost no similarity to the ancestral architecture. Conclusions Longidoridae exhibited more rearranged mitogenomic architecture than the hypervariable Mermithidae. Similar to the Chromadorea, the evolution of mitochondrial architecture in enoplean nematodes exhibits a strong discontinuity: lineages possessing a mostly conserved architecture over tens of millions of years are interspersed with lineages exhibiting architectural hypervariability. As Longidoridae also have some of the smallest metazoan mitochondrial genomes, they contradict the prediction that compact mitogenomes should be structurally stable. Lineages exhibiting inverted skews appear to represent the intermediate phase between the Trichinellidae (ancestral) and fully derived skews in Chromadorean mitogenomes (GC skews = 0.18 to 0.64). Multiple lines of evidence (CAT-GTR analysis in our study, a majority of previous mitogenomic results, and skew disruption scenarios) support the Dorylaimia split into two sister-clades: Dorylaimida + Mermithida and Trichinellida. However, skew inversions produce strong base composition biases, which can hamper phylogenetic and other evolutionary studies, so enoplean mitogenomes have to be used with utmost care in evolutionary studies.

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.

Labronema Thorne, 1939 is a large and diverse dorylaimid genus with complicated taxonomy. Two new species, Labronema porosum sp. nov. and Labronema bidoupense sp. nov. from natural habitats in Vietnam were characterised both morphologically and molecularly (18S rDNA and 28 rDNA), and line drawings and microphotographs are provided. Phylogenetic analyses showed that the new species clustered together with Labronema ferox Thorne, 1939, the type species of the genus. The two new taxa belong to a group of Labronema species with medium body (L = 1.5–2.5 mm) and odontostyle (31–39 μm) length, and a lip region offset by a constriction. Based on morphological and molecular evidence, this study shows that the populations from Vietnam previously identified as L. glandosum Rahman, Jairajpuri, Ahmad & Ahmad, 1986 in fact represent L. porosum sp. nov. Evolutionary relationships of Labronema species are discussed. A key to the species of Labronema with a medium-sized odontostyle (31–39 μm) is provided as well as a list of the species of the genus considered valid.

The diversity and spatial distribution of microscopic invertebrates in the Arctic have yet to be studied in detail. Knowledge of this is especially important in the context of glacier shrinking, one of the most visible environmental consequences of climate change. To understand how time since deglaciation shapes the communities of limno-terrestrial microfauna, we analysed samples of moss collected during the summer of 2021 in forefields of Trygghamna (Svalbard), where glaciers thought to have started to recede at the beginning of the twentieth century. We estimated the taxonomic and trophic composition and abundance of all microfauna groups (with a specific focus on little-known bdelloid rotifers) in two areas, which correspond to the different stages of the glacial retreat. The impact of 14 other environmental parameters (distance from the sea, moisture, moss structural complexity, soil nutrient, and isotopic composition) was considered. Thirty-seven microfauna taxa were found, wherein Dorylaimida nematodes (Dorylaimida, Nematoda) dominated both in frequency (present at all sites) and abundance (50 ± 21% from all individuals). Less prevalent bdelloid rotifers (Bdelloidea, Rotifera) were followed by tardigrades (Tardigrada), which, in contrast to others, were more abundant in the later deglaciated area. In general, environmental parameters explained 81.8% of the microfauna distribution. Time since deglaciation was the most significant factor (9.5%). Among the variables that act at a fine scale, the most important were moisture in the habitat (6%), presence of ground in the samples (4%), and δ15N (4%). The moss structural complexity did not have a significant effect, and neither did most of the variables characterising soil nutrient and isotopic composition. However, some variability was observed for different lower taxa.

During a nematological survey in the Western Ghats a new nematode belonging to the superfamily Tylencholaimoida (Dorylaimida) extracted from the rhizosphere of the soil of grasses, is described and illustrated. Tahamina indica gen. nov. , sp. nov. is characterized by females with a body length of 1.3–1.4 mm; lip region 8.0 μm wide, approximately one-fourth of the body diameter at the pharyngeal base; amphidial fovea cup-shaped, about one-half as wide as the lip region diameter. Odontostyle 8.0–9.0 μm long, 1.0–1.1 times lip region diameter; guiding ring simple; odontophore rod-like, 10.5–11.5 μm long with basal thickening or minute knobs-like structure; pharynx consisting of a weakly muscular anterior part, expanding abruptly into a cylindrical basal bulb, occupying about two-fifths to one-half of the total pharyngeal length; female genital system monodelphic-opisthodelphic with anterior uterine sac; vulval opening pore-like, and tail elongated with a slight dorsally curved tip. Males not found.

Aporcelaimellus obtusicaudatus was recovered from mustard and sugarcane fields of Uttar Pradesh and Uttarakhand, India. The present species was identified through morphology, molecular and phylogenetic analysis. The Indian populations are characterized by having females with a body length (1.7–3.4 mm), lip region (4.9–8.8 µm), Amphids 6–9 µm, odontostyle length (15.7–26.4 µm), neck length (374.6–745.1 µm), pharyngeal expansion occupying 45–60% of neck length, simple uterus (67.4–124.3 µm), V = 49.1–58.7, female tail (32–44.9 µm, c = 41.1–105, c ' = 0.5–1.3) with short, conoid, rounded terminus to convex conical. The molecular phylogenetic analysis based on 18S and 28S rDNA revealed A. obtusicaudatus as a paraphyly. The present populations of Indian A. obtusicaudatus (OM269524; OP020675) placed close to deposited Indian sequence (OP048816; OP048823) and Slovakian populations of A. obtusicaudatus (MH206119). The result of 28S rDNA phylogeny showed that the present population (OM258706) placed close to other populations of the same species from India (OM418794) with 0.55 posterior probability supports. The haplotype analysis based on 28S rDNA revealed 6 haplotypes, which displayed low nucleotide (π = 0.013) diversity. In contrast, haplotype diversity (Hd) was 1.00, and the number of segregating sites (S) was 14. The phylogenetic analysis grouped the various populations into two clades, and the result showed German populations placed into two clades, which showed high variability in haplotype supported by the haplotype network. Tajima (D) and Fu’s Fs were found to be negative ( P > 0.05), whereas the overall FST value was 0.31040 ( P = 0.118). In conclusion, genetic analysis revealed 31.04% variation among groups/populations and 68.95 within populations, indicating a low genetic variation between the same populations of A. obtusicaudatus belonging to the same country.

The taxonomic position of two antarctic dorylaimid species Amblydorylaimus isokaryon (Loof, 1975) Andrássy, 1998 and Pararhyssocolpus paradoxus (Loof, 1975), gen. n. , comb. n. are discussed on the basis of morphological, including SEM study, morphometric, postembryonic and sequence data of 18S rDNA and the D2-D3 expansion fragments of large subunit rDNA. The evolutionary trees inferred from 18S sequences show insufficient resolution to determine the assignment of the two species to particular families, moreover Pararhyssocolpus paradoxus gen. n. , comb. n. (=Rhyssocolpus paradoxus ) previously regarded as a member of Nordiidae or Qudsianematidae, showed distant relationship both to Rhyssocolpus vinciguerrae and Eudorylaimus spp. The phylogram inferred from 28S sequences revealed that Amblydorylaimus isokaryon is a member of a well-supported group comprised of several Aporcelaimellus spp., while, no close relationships could be revealed for the Pararhyssocolpus paradoxus gen. n. , comb. n. to any nematode genus. On the basis of molecular data and morphological characteristics, some taxonomic changes are proposed. Amblydorylaimus isokaryon is transferred from family Qudsianematidae to family Aporcelaimidae, and a new monotypic genus Pararhyssocolpus gen. n. is proposed, attributed to Pararhyssocolpidae fam. n. The diagnosis of the new family is provided together with emended diagnosis of the genera Amblydorylaimus and Pararhyssocolpus gen. n. Data concerning distribution of these endemic genera in the Antarctic region are also given.

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.

A new species, , extracted from the rhizosphere soil of unidentified grasses from Helan Mountain, Inner Mongolia, China was identified. The new species is characterized by having a body length of 0.93-1.07 mm with the lip region approximately one-quarter of the body diameter at the posterior end of the neck region wide; female didelphic-amphidelphic; pars proximalis vaginae violin-shaped. Males were not found. SEM observations of the new species were made and a phylogenetic analysis of both the 18S rDNA and the D2-D3 region of 28S rDNA is presented.