Oligochaetes and chironomids are considered by many authors as biological indicators of environmental conditions and are represented for a great species diversity in the benthic, pleuston and periphyton communities of different habitats. Eighty one species of oligochaetes are reported from the Paraná River, sixty two species of Naididae, twelve Tubificidae, three Opystocistydae, one Narapidae, two Haplotaxidae and one Alluroididae. Narapa bonettoi Righi and Varela, 1983, Haplotaxis aedeochaeta Brinkhurst and Marchese, 1987, Paranadrilus descolei Gavrilov, 1955, Brinkhurstia americana (Brinkhurst, 1964), Slavina evelinae (Marcus, 1942), Limnodrilus neotropicus Cernosvitov, 1939, Trieminentia corderoi (Harman, 1969), Dero righii Varela, 1990 are endemic species of the Neotropical region. The knowledge of Chironomidae is very scarce and twenty genus were reported of Chironominae, seven Tanypodinae, and seven Orthocladiinae. The species cited in the Paraná basin are Chironomus xantus Rempel 1939, Chironomus calligraphus Goeldi, 1905; Goeldichironomus holoprasinus Goeldi, 1905; G. natans Reiss, 1974; Parachironomus supparilis (Edw. 1931) var. longistilis (Spies et al, 1994).