A new nematode, Myleusnema bicumis gen. et sp. п., is described from the intestine of a characoid freshwater fish, Myleus ternetzi (Norman, 1929) (Cypriniformes: Serrasalmidae), from French Guiana. This cosmocercoid nematode species represents a new genus of the family Kathlaniidae, being characterized mainly by the shape of the body (the cephalic portion is separated from the rest of the body at the level of the nerve ring), structure of the cephalic extremity (presence of three lips and three lamella-like formations demarcating the buccal cavity), absence of an oesophageal pharynx, presence of medium-sized alate spicules (0.694-0.721 mm long), two conspicuous postcloacal homs associated with a gubernaculum, and by the number and distribution of caudal papillae in the male.
A new kathlaniid nematode, Myleusnema brasiliense sp. n„ is described from the intestine of a characoid fish, Myleus sp. (Serrasalmidae, Cypriniformes), from Brazil, It differs from the only other congeneric species Myleusnema bicornis Moravec et Thatcher, 1996 mainly in having an unseparated cephalic portion of the body, lips provided with Hanges with numerous spikelike appendages, deirids situated more posteriorly, more numerous (8 pairs) subventral preanal papillae in the male, and distinctly longer spicules (1.58-1.70 mm). The species description is based on light microscopic and scanning electron microscopic (SF,M) observations.