Six species of the genus Tylencholaimellus, one new and five known, collected in virgin and cultivated soils of East Azarbaijan province, Iran, are studied. Tylencholaimellus zeinabadensis sp. n. is morphologically characterised by its 1.2-1.7 mm long body, lip region 10-13 μm wide and offset by deep and broad constriction, odontostyle 16-20 μm long, stylet 22-30 μm long, neck 186-234 μm long, pharyngeal bulb 30-43 μm long, anterior uterine sac 55-103 μm long or 0.9-1.7 corresponding body diam. long, V = 34-41, tail short and rounded to conoid (20-30 μm, c = 45-83, c = 0.5-1.0), spicules 39-50 μm long, and one or two ventromedian supplements with hiatus. Molecular analyses using the D2-D3 expansion regions of the 28S rRNA gene sequences of the new species confirmed the monophyly of this genus based upon currently available data. A population of T. affinis is described and illustrated, and new data (morphometrics, pictures and distribution) are provided for T. loofi, T. paracinctus, T. polonicus and T. striatus.
