Rotifers of the upper Paraná River floodplain: additions to the checklist.

Rotifers present a high diversity in freshwater ecosystems. This study registered 11 genera and 42 species, new records for the Upper Paraná River floodplain. These results showed an increase in rotifer diversity in this ecosystem from 184 to 230 species. Among them some were registered only in the rivers and others in the lagoons. Thirty-seven species occurred in the littoral zone and 34 species in the pelagic; 3 species were registered only in the former zone and 2 species only in the latter. The lagoons presented the greatest richness, probably because of the greater stability, low current velocity, and the extensive aquatic macrophyte banks in the littoral zone of these environments as compared to those of the rivers. The highest number of species in the littoral habitats occurred due to the greater influence of shoreline vegetation, which allows greater habitat diversification. This fact contributed to the occurrence of non-planktonic species in the zooplankton samples.