Resumo: Testudinella é um táxon de Rotifera amplamente distribuído no Brasil. Em recentes coletas em lagos marginais conectados ao rio Paranapanema (São Paulo, Brasil), nós encontramos espécimes de Testudinella mucronata e T. patina com concavidades em suas lóricas. O objetivo do estudo foi descrever as concavidades observadas em indivíduos de ambas as espécies e discutir suas possíveis causas. Amostras de plâncton foram coletadas em duas estações de amostragem, na zona pelágica (PZ) e litorânea (LZ) dos lagos Panema e Coqueiral; ambos os lagos são ultra-oligotróficos e não poluídos. Para T. mucronata, 4% dos indivíduos com concavidades foram encontrados na PZ do lago Coqueiral e 50% na LZ do lago Panema. Em T. patina, a proporção de espécimes com concavidades correspondeu a 34% na LZ do lago Panema e 17% na PZ do lago Coqueiral. Nesse estudo, nós sugerimos que baixas temperaturas da água, eventos de predação e/ou recente eclosão são fatores que podem justificar as concavidades na lórica dos espécimes do nosso trabalho.

Abstract: Testudinella is a taxon of Rotifera broadly distributed in Brazil. In a recent collection in marginal lakes connected to the Paranapanema River (São Paulo, Brazil), we found specimens of Testudinella mucronata and T. patina with concavities on their lorica. The objective of this study was to describe the concavities observed in individuals of both species and discuss their possible causes. Plankton samples were collected at two sampling stations, in the pelagic (PZ) and littoral (LZ) zones of the Panema and Coqueiral lakes; both of these lakes are ultra-oligotrophic and not polluted. For T. mucronata, 4% of individuals with concavities were found in the PZ of Coqueiral lake and 50% in the LZ of Panema lake. In T. patina, the proportion of specimens with concavities corresponded to 34% in the LZ of Panema lake and 17% in PZ of Coqueiral lake. In this study, we discussed that low water temperatures, predation events and/or recent hatching are factors that may justify the concavities in the lorica of specimens of our work.

This study evaluated the isotopic composition of three zooplankton species - Notodiaptomus amazonicus (Wright, 1935), Moina minuta Hansen, 1899 and Bosmina hagmanni Stingelin, 1904 - from the Upper Paraná River floodplain. We predicted that there would be isotopic variability among species in the different sampled environments. Samplings were conducted in three lakes from the Baía subsystem and in two lakes from the Paraná subsystem. At each location, some abiotic variables were measured, and zooplankton (3 to 4) and phytoplankton (3) samples were taken. The species sampled did not present significant differences between subsystems; however, they were different among the lakes, with variations of about 10.8‰ for δ13C and 5.8‰ for δ15N. The isotopic values found for phytoplankton also did not differ significantly among sampling stations, presenting variations of about 9.3‰ for δ13C and 7.4‰ for δ15N. These results indicate that the isotopic values of species varied among the lakes, and that they are dependent on isotopic signals from phytoplankton.