A new species of allocreadiid digenean is described from Priapichthys annectens (Regan) (Osteichthyes: Poeciliidae) in the Área de Conservación Guanacaste, Costa Rica. A new genus, Paracreptotrema, is proposed to accommodate this species as well as Fellodistomum mendezi Songandares-Bernal, 1955, which was previously described from another poeciliid, Brachyrhaphis episcopi, in Panama. Paracreptotrema differs from all other nominal genera of Allocreadiidae by a combination of its symmetrical testes, restricted vitellaria, and the lack of oral lappets (muscular ‘papillae’) or other such appendages. Paracreptotrema blancoi n. sp. resembles Creptotrema creptotrema Travassos, Artigas and Pereira, 1928, but differs in lacking ventral oral lappets and in having vitellaria extending posteriorly only to the level of the testes. It can be distinguished from P. mendezi n. comb. in having a relatively larger and more posteriorly placed acetabulum, vitellaria that are more restricted anteriorly, smaller testes, and a uterus that does not extend to the posterior end of the body. The genus seems to be restricted to poeciliids in Central America.