O presente trabalho explora os aspectos taxonomicos, ecologicos, morfologicos, biometricos e biogeograficos dos Arcellinida Kent, 1880 coletados no Parque Ecologico do Rio Tiete, Sao Paulo Brasil. Foram encontrados organismos pertencentes a cerca de 30 taxons nominais, no entanto, a revisao da literatura, novos dados morfologicos obtidos atraves do Microscopio Eletronico de Varredura e medidas biometricas realizadas com grande numero de individuos permitem afirmar que muitos destes taxons estao se referindo a mesma entidade na natureza. Logo, na presente pesquisa sao descritas, com detalhes de distribuicao geografica, morfologia ultra-estrutural, morfometria e ecologia, especies pertencentes a quatro familias e cinco generos: Difflugia corona Wallich, 1864; Difflugia gramen Penard, 1902; Difflugia lanceolata Penard, 1890; Difflugia claviformis Penard, 1899; Difflugia gigantea Chardez, 1967; Centropyxis aculeata (Ehrenberg, 1838); Netzelia wailesi (Ogden, 1980); Lesquereusia modesta Rhumbler, 1895; Lesquereusia mimetica Penard, 1911; Arcella hemisphaerica Perty, 1852; Arcella gibbosa Penard, 1890; Arcella discoides Ehrenberg, 1871 e Arcella brasiliensis Cunha, 1913. Sao discutidas inovacoes taxonomicas para que a comparacao de dados obtidos usando tecnicas atuais com aqueles reportados na literatura tradicional seja feita da maneira mais explicita possivel, de modo a delimitar melhor o conceito taxonomico de cada especie abordada.

The present survey explores the taxonomic, ecologic, morphologic, biometric and biogeographic aspects of the Arcellinida Kent, 1880 collected at the Ecological Park of the Tiete River, Sao Paolo Brazil. Around 30 nominal taxa were identified, however, a review of the literature and new morphologic data obtained via the Scanning Electron Microscope and biometric measures with a large number of individuals allow the inference that many of these taxa are referring to the same natural entity. Therefore, the present work describes species from four families and five genera, along with details about geographic distribution, ultra-structural morphology, morphometry and ecology: Difflugia corona Wallich, 1864; Difflugia gramen Penard, 1902; Difflugia lanceolata Penard, 1890; Difflugia claviformis Penard, 1899; Difflugia gigantea Chardez, 1967; Centropyxis aculeata (Ehrenberg, 1838); Netzelia wailesi (Ogden, 1980); Lesquereusia modesta Rhumbler, 1895; Lesquereusia mimetica Penard, 1911; Arcella hemisphaerica Perty, 1852; Arcella gibbosa Penard, 1890; Arcella discoides Ehrenberg, 1871 e Arcella brasiliensis Cunha, 1913. Taxonomic innovations are discussed in order to make comparison of recent data with those reported on traditional literature a more explicit practice, allowing a better understanding of each species taxonomic concept.