New reports and a redescription of Porrocaecum heteropterum (Diesing, 1851) (Ascarididae), a rare nematode parasitic in South American threskiornithid birds

Porrocaecum heteropterum (Diesing, 1851) (Nematoda, Ascarididae) is reporte d parasitising the white-faced ibis Plegadis chihi and the black-faced ibis Theristicus melanopis melanopis (Ciconiiformes, Threskiornithidae) from th e Provinces of Buenos Aires and Neuquen, Argentina. This nematode has been reported very few times in the literature, mainly from Brazilian threskiorn ithids, and there have been no new reports following a redescription of the species given in 1957. This paper provides new host and locality records f or this rather rare species, as well as some additional morphological data, mainly based on SEM studies, which complement the previous descriptions. T he scarce and sporadic records of this species seem to indicate not only a defined host-specificity towards threskiornithid birds but also that the ac quisition of this parasite is possible only when certain ecological barrier s, including food availability, feeding habits and environmental conditions , are surmounted.