Macielia jorgei n. sp. is described from Chaetophractus vellerosus from La Rioja, Argentina. Also Trichohelix tuberculata is redescribed in detail. The new species is characterized by parasitizing the small intestine, possessing a bursal membrane and telamon, having complex and sclerotized spicules distally divided into 2 processes, a simple, poorly sclerotized gubernaculum, and synlophe with bilateral symmetry and 12 cuticular ridges. This is the second report of a species of Macielia in Argentina. The synlophe of Trichohelix tuberculata is asymmetric and is characterized by 3 ventral ridges, oriented to the left. The size of these ridges decreases until they disappear at midbody.