Summary The genus Sakia is recorded from Iran for the first time and Sakia arboris n. sp., recovered from two geographical points in northern Iran, is described. The new species is characterised by its smooth cuticle under light microscopy (LM), absence of lateral fields, head continuous with body contour, flattened lip region, 9.3 (9.0-10.0) μm long stylet, vulva at 60.2 (59.3-61.3)%, bilobed spermatheca, 117 (102-128) μm long tail, and 14.3 (14-15) μm long spicules. By lacking lateral fields, the new species comes close to three known species of the genus, namely: S. alii, S. castori and S. indica. Molecular phylogenetic analyses using sequences of the near full-length fragment of the small subunit of ribosomal DNA (18S rDNA) and the D2-D3 expansion segments of the large subunit ribosomal DNA (28S rDNA) were performed using Bayesian inference (BI) and maximum likelihood (ML) methods. In the reconstructed Bayesian tree using the 18S rDNA sequence of the type population, the new species occupied a position in a clade including two isolates of Sakia sp. and some species of Lelenchus, with maximal BPP and high ML BS values (1.00/99%). In the reconstructed 28S rDNA phylogenetic tree, two newly sequenced isolates of S. arboris n. sp. formed a well-supported clade with Lelenchus spp.

Labrys khuzestanensis n. sp. was recovered from the rhizosphere of a palm tree in southwestern Iran and described using morphological and molecular data. The new species was characterized by combination of the following features: its 590–675 μm long body, finely annulated cuticle in light microscopy (LM), lateral field with two smooth incisures, cephalic region dorso-ventrally flattened with protuberant, elongate and laterally extended labial plate, appearing a V-shaped piece in lateral view, amphidial openings as longitudinal slits confined to labial plate in scanning electron microscopic (SEM) images, stylet 7.5–9.0 μm long, elongated fusiform median bulb with faint valvular apparatus, excretory pore wide with moderately sclerotized duct and elongate filiform tail with finely rounded tip. Compared to four currently known species under the genus, the new species has a remarkably larger and more prominent labial plate as revealed by SEM and trapezoid cephalic region under LM. The molecular phylogenetic analyses of the new species using partial SSU rDNA revealed it has close affinity with three species of Labrys (L. chinensis, L. fuzhouensis and L. filiformis) in Bayesian inference (BI) and maximum likelihood (ML) methods and occupied a placement inside their clade. L. fujianensis, the other species of the genus, occupied a distant placement to the aforementioned clade. This is the second species of Labrys being originally described from Iran, representing the third species of Labrys occurring in the country.

Xiphinema castilloi sp. n., a new species of morphogroup 5 sensu Loof & Luc, 1990, is described and illustrated based on morphological, morphometric and molecular data. The new species is characterised by a 4.2-5.0 mm hody assuming an open C to J shape after heat fixation, lip region separated from the body by a shallow depression, a 101-126 /xm odontostyle, two equally developed genital tracts with pseudo-Z-organ in uterus (8-11 globular structures) and devoid of spines, tail dorsally convex conoid with a muero, presence of functional males, and four Juvenile developmental stages. By having two equally developed genital tracts, presence of pseudo-Z-organ, and similarities in tail shape of females and juveniles, the new species comes more close to X. artemisiae, X. diversicaudatum, X. erriae, X. jomercium, X. lapidosum, X. lusitanicum and X. ripogranum. The Bayesian inference (BI) and Maximum Likelihood (ML) analyses using 707 bp partial sequences of D2-D3 segment of 28S rDNA placed the new species in a monophyletic group with X. dentatum, another member of morphospecies group 5 with 1.00 Bayesian posterior probability (BPP).

Molecular data on several species of trichodorids occurring in Iran are provided. Live specimens of two species, Trichodorus arasbaranensis and T. gilanensis, were collected from their type localities. One population of T. orientalis was collected from Arasbaran forests in Eastern Azarbayjan province. The species Paratrichodorus porosus, occurring in Gilan province, and one European isolate of P. pachydermus were also included in phylogenetic analysis. An Iranian population of T. minzi, representing only the second population found of this rare species, was recovered from soil samples collected from grasslands of north-western Iran and is in morphological congruence with the original description of the species. Besides morphological study, molecular phylogenetic study was performed on newly reported species using partial 28S rDNA data, and the phylogenetic relations of all sequenced species as inferred from Bayesian analysis are discussed. According to the phylogenetic tree, two newly described species, T. golestanensis and T. iranicus, formed a clade and further studies revealed they have the same morphology and molecular sequences of 28S rDNA D2-D3. Accordingly, T. golestanensis is regarded as a junior synonym of T. iranicus according to the Principle of Priority.

Trichodorus variabilis, recovered from three separate locations in natural forests of northern Iran, was studied using morphological, morphometric and molecular data. Variation in position of the ventromedian cervical papillae (CP1 and CP2) with respect to the onchiostyle base in the resting position, and spicule characters (having or lacking striation in distal blade region and bristles in proximal blade region) were observed. Variation was also observed in the nature of the pharyngo-intestinal junction (offset to slight overlapping). The secretory-excretory pore of females also showed slight variation in placement. Molecular phylogenetic studies, using partial 28S rDNA D2-D3 sequences of three studied populations and one sequenced isolate of the species from Greece, revealed T. variabilis has variation in the sequences of this genomic fragment. The similarity percent of four sequences ranged from 96.7 to 99.7%. The species was found for the first time outside of Greece, the country from which it was originally described. A newly recovered population of T. persicus, originally described from Iran, was also included in the molecular phylogenetic analyses.