Two hairworms from Argentina, Gordionus porosus n. sp. and Gordionus ondulatus (Nematomorpha, Gordioidea), are described and illustrated. The cuticle of both species shows only 1 areolar type. Areoles of G. porosus are polygonal and surrounded by minute bristles and the interareolar groove is wide and with large pores. Gordionus ondulatus is characterized by rectangular or irregular areoles from which margins cuticular elongations project as finger-like structures, giving an undulated appearance. Comparing these species to the remaining American species of Gordionus, G. porosus is close to Gordionus violaceus by virtue of the large number of small bristles surrounding the areoles and can be distinguished by the shape of these bristles and by the arrangement and shape of the areoles. Gordionus ondulatus differs from the other species of the genus by its undulating margins. Giordinus lineatus and Giordinus violaceus have been reported in North America, Giordinus platycephalus in North and Central America, Giordinus capitosulcatus in Central America, and Giordinus prismaticus, G. ondulatus, and G. porosus only in South America.