AbstractTrachyglossus quintus gen. n., sp. n. is described from Charactopygus frequens from Zaire. The new genus is characterised by having a dorsoventrally elongate oral aperture with the dorsal jawplate developed into a tongue-like rasp extending over halfway down the corpus lumen; a hypertrophied corpus and isthmus; well developed, lobate caudal alae in the male; hypertrophied, lobiform, vulval flap and by the form of the spicules and disposition of the copulatory papillae. It is closest to Xustrostoma, a genus with which it shares the development of a tongue-like rasp, but differs principally in the hypertrophy of the pharyngeal components: in Trachyglossus gen. n. it is the corpus and isthmus which are enlarged whereas in Xustrostoma it is the basal bulb. Trachyglossus gen. n. also differs in having strongly developed, lobate, caudal alae in the male (vs absent) and in possessing a lobiform anterior vulval lip. It differs from Obainia in having the dorsal jaw plate modified to form a tongue-like rasp, corpus and isthmus region of pharynx hypertrophied (vs basal bulb in African species of Obainia), hypertrophied vulval flap, form of spicules, distribution of copulatory papillae and presence of caudal alae in the male. From Zalophora it differs in the form of the pharynx, development of a tongue-like dorsal rasp instead of numerous teeth on the dorsal jawplate, presence of a hypertrophied vulval lobe and in being amphimictic instead of parthenogenetic. Xustrostomatidae fam. n. is proposed for all those genera (formerly included in the Rhigonematidae) with the cephalic capsule laterally compressed to form a dorsoventrally orientated oral aperture. Rhigonema multipapillatum (Skrjabin, 1916), previously known only from the original description, is redescribed and established as a valid species on the basis of material from Uganda. A neotype is proposed. The species is characterised by medium body size; posterior margin of cephalic collar fused to body; presence of fine microtrichs in the cervical region; cuticularised mouth plates clothed in minute spine-like structures; Type 1 female genital tract; conoid spicate tail shape in both sexes; form of the long, slender spicules and disposition of the 31 copulatory papillae, three postcloacal pairs of which being subdorsal or sublateral in position.