New species of Trichuris (Nematoda: Trichuridae) parasitizing Heteromys salvini (Rodentia: Heteromyidae) from Costa Rica, with a key to Trichuris species described from Heteromyidae.

Trichuris guanacastei n sp., a parasite isolated from the Salvin' spiny mouse Heteromys salvini, collected from the Guanacaste Conservation Area, Costa Rica, during February 1996 is described. The new species was compared morphologically with the 29 known species that parasitize rodents distributed in 12 families in North and South America; T. guanacastei n. sp. it is characterized by the following set of traits: presence of a spicular tube (measuring 0.72-0.99); thick proximal cloacal tube and a short distal cloacal tube with a total length of 0.72-1.36; eggs 0.03-0.05 long and a semi-protrusible vulva. The new species represents the first one described in the genus in Costa Rica and the fifth one described in the Americas that parasite Heteromyidae.