گزارش چهار گونه از جنس Yeates, 1967 Crassolabium از جنوب شرق شهرستان خرم‎آباد، استان لرستان، ایران

During the study of free-living nematodes fauna of southeast of Khorramabad county in 2022 and 2023, several soil samples were collected from the rhizosphrere of oak trees. Following the extraction of nematodes from the soil samples using modified Whitehead tray method, nematodes were killed and fixed by the De Grisse method and permanent slides prepared as well. Based on the morphological, morphometric and molecular (sequence of the D2-D3 region of 28S rDNA) characteristics of the specimens, four species of the genus Crassolabium including C. pumilum, C. rhopalocercum, C. circuliferum and C. angulosus were identified and the accession numbers PP971543, PP971541, PP971544 and PP971540 registered in the Gene Bank, repectively. Among the identified species, C. angulosus is a new record for the nematode fauna of Iran. The species is distinguished by cylindrical body, 1.63-1.77 mm length, open C-shape when heat relaxed and slightly curved ventrad, lip region angular and offset by marked depression, 13.5-14.0 µm wide or 2.0 to 2.5 times of its height, lips slightly amalgamated with protruding papillae, amphid fovea cup-like, amphidial aperture situated at the level of head base, 5.5-6.5 µm wide, odontostyle and odontophore 13-15 and 20-28 µm long, respectively, guiding ring simple and delicate, anterior part of esophagus muscular and cylindrical, pharyngeal expansion 157.5-180.0 µm long, cardia conical, genital system didelphic-amphidelphic, opposed, vulva longitudinal with two glandular cells present near the vagina, prerectum 2.5-3.0 anal body width long, rectum 35.5-38.5 µm long, tail rounded to conoid and dorsally convex. In phylogenetic tree none of the sequences belonging to this genus form a separate clade together and on the contrary, have different position in topology of evolutionary tree derived from this study. Other researchers have considered Crassolabium as polyphyletic genera.