Morphology of the nematode Deletrocephalus dimidiatus Diesing, 1851 from the rhea, Rhea americana Linnaeus, 1758, together with a key to species of Deletrocephalinae.

The family Deletrocephalidae consists of three species, from two genera: Deletrocephalus dimidiatus, D. cesarpintoi and Paradeletrocephalus minor, which differ from one another in terms of the buccal capsule structure, the dorsal ray from the male copulatory bursa and the length of the vagina in the female. All these species are parasites of the gastrointestinal tract of the rhea, Rhea americana. Only D. dimidiatus was reported to be a parasite of the other rhea species, Darwin's rhea, R. pennata. Currently, there are no studies on the ultrastructure and biology of these parasites or their pathogenicity in these birds. Thus, the present study aimed to examine the ultrastructure and add more details of the morphology of D. dimidiatus from R. americana. Four adult rheas were necropsied, and the gastrointestinal tract was collected and examined for the presence of parasites. Nematodes were analysed by optical and scanning electron microscopy (SEM). All birds were parasitized by D. dimidiatus. Some morphological and morphometric characters were observed that differ from reports of other studies of this species by other authors. In addition, new details were added, well described by SEM, and a key to the species of the subfamily Deletrocephalinae is given.