Mazzanema n. gen. and Mazzanema fortuita n. comb. for Longistriata fortuita Freitas, Lent, and Almeida, 1937 (Nematoda: Heligmonellidae), a parasite of the marsh rat Holochilus chacarius (Rodentia: Cricetidae) from northern Argentina.

The species described as Longistriata fortuita Freitas, Lent, and Almeida, 1937 is here redescribed from new material collected from the type host, Holochilus chacarius balnearum Thomas, and the type locality, San Martín del Tabacal, Salta, Argentina. Neotypes are designed for the species since the type material deposited by the authors is lost. The original description did not include the synlophe or the female and both are here described. Several characters of the synlophe as the number of ridges (14-19), the ridges continuous and all around body, and the presence of a gradient of size of the ridges allow us to place the species within the Heligmonellidae, Nippostrongylinae. The species possesses a unique combination of characters as the synlophe having a carene together with characters of the caudal bursa as the pattern 1-3-1 and the strong development of the dorsal lobe and ray, which precludes its inclusion in any known genus of Nippostrongylinae. A new genus Mazzanema n. gen. is proposed for it, resulting in the new combination Mazzzanema fortuita n. comb.