Contribuição ao conhecimento da helmintofauna de raias fluviais (Paratrygonidae: Chondrichthyes)

Abstract

The classification and distribuition of Brazilian freshwater Paratrygonidae stingrays are presented according to FOWLER (1948), as well as some data concerning biology of elasmobranchs. 2. Four species of Cestode are redescribed: Rhinebothrium paratrygoni Rego & Dias, 1976; R. scorzai Lopez-Neyra & Diaz-Ungria, 1958; Acanthobothrium terezae Rego & Dias, 1976 and Eutetrarhynchus araya Woodland, 1934). 3.Two new species in the Tetraphyllidea (Cestoda) are proposed: Rhinebothrium freitasi sp. n. (Phyllobothriidae) and Potamotrygonocestus travassosi sp. n. (Onchobothriidae). Both are compared to those ocurring in freshwater rays (Tables I and II). 4. Two free proglottids were found as well as a juvenile form with the appearence of a plerocercoid but were not identified. This suggests that at least two more unkonwn Tetraphyllidean species may occur in P. hystrix. 5. Leiperia gracile (Pentastomida) is reported for the second time in stingrays; Diesing was the first to observe it in 1835. P. motoro is an intermediary host for this pentastomid. 6. A complete account of Leiperia gracile (Diesing, 1835) is presented since Diesing's first report, dealing with Brazilian material recovered by Natterer. The validity of species is also discussed. -52- 7. Brevimulticaecum sp., a nematode genus usually ocurring in African and South American crocodiles, is reported/ for the first time in an elasmobranch host. The samples appear/ to belong to a new species but were infortunately poorly preserved, so that a complete diagnosis could not be provided. 8. Attention is paid to the special conditions of osmotic pressure observed in the spiral valve of marine elasmobranchs. For this reason, this site is unfavourable for most of the helminth fauna, even the Cestodes, except for Trypanorhyncha/ and Tetraphyllidea. 9. The Paratrygonidae are freshwater rays, which, as elasmobranchs, have definitely returned to this habitat, as they show physiological adaptations differing totally from their/ marine relatives; the former are not able to concentrate urea, even in dilutedsalt water. This suggests that they can be related to teleosts from the same habitat. 10. Some form of physiological adantation udergone by the helminths with reference to the osmotic conditions of freshwater rays could not be demonstrated. At least, mopnhological modifications are not observed in marine and freshwater Tetraphyllidoe. 11. Comments on the phylogeny of helminthic groups are made; the Tetraphyllideans seems to be the most ancient among the Cestodes, giving rise to the other known Orders. Brevinulticaecum (Nematoda) parasitism is considered as recent in these rays. 12. Considerations on the Pentastomid, mainly on Leiperia gracile are made, as well as on the parasitic fauna of rays and crocodiles; Gondwanland and Continental Drift are important concepts in any discussion of phylogenetic relationships.