Diagnosis ( Dorylaimida: Tylencholaimidae): Small sized nematodes, between 0.3 and 1.2 mm in length. Cuticle tylencholaimoid, with irregular radial refractive elements; outer layer generally with fine transverse striations. Lip region always cap-like, offset by constriction or sometimes by depression; lips more or less amalgamated, with the perioral area either transformed into a disc-like structure or not. Cheilostom a truncate cone, often with perioral thickenings. Amphid aperture slit-like, about half as wide as corresponding lip region diameter. Odontostyle somewhat shorter than lip region diameter, its aperture about one-fourth to one-third of total length. odontophore rod-like, with more or less distinct basal knobs. Pharynx consisting of anterior slender part extending gradually or abruptly into the basal expansion with thickened inner lining, which occupies one-third to two-fifths of the total neck length. Cardia usually hemispheroid to rounded-conoid. Female genital system amphidelphic, monoprodelphic or mono-opisthodelphic. Vulva transverse. Males with dorylaimoid spicules, lateral guiding pieces and a few spaced (very rarely numerous and contiguous) ventromedian supplements. Tail similar in sexes, elongateconoid to hemispherical.