Chimaerula bonai sp. n. is described from the small Intestine of Phimosus infuscatus (Lichtenstein) in Paraguay. The new species differs from the other two species of Chimaerula Bona, 1994, i.e., Chimaerula woodlandi (Prudhoe, 1960) and Chimaerula leonovi (Belogurov et Zueva, 1968), mainly by the intermediate number of rostellar hooks (30-34 compared to 42-46 in the former and 20-22 in the latter), longer rostellar hooks (31-34 pm versus 26 pm and 19-21 pm, respectively), shorter cirrus sac (58-82 pm versus 158-201 pm and 134-183 pm, respectively) and the absence of rosethorn spines in the cirrus armament. Modifications in the generic diagnosis of Chimaerula are proposed in order to conform it with some peculiarities of the new species (i.e., the relatively small and thin cirrus, the absence of rosethom spines in its armament and the small cirrus sac).