During an ecological study of the epibiotic relationship between ciliate protists and Pomacea figulina (Spix, 1827) (Gastropoda, Ampullariidae), originating from an urban stream in southeast Brazil, a high infestation by the peritrich ciliate Carchesium polypinum (Linnaeus, 1758) Ehrenberg, 1830 (Ciliophora, Peritrichia) associated to the shell of one mollusc among 23 was observed. We provided a morphological and morphometric study of C. polypinum using observations of specimens in vivo, after protargol staining, and examined using scanning electron microscopy. The Brazilian-population of C. polypinum is characterized by: size of zooid in vivo 89 µm x 57 µm on average; colony regularly dichotomously branched with usually up to 40 zooids; macronucleus usually J-shaped; single contractile vacuole located in the upper third of body; myoneme not continuous throughout the colony; stalks contract despite the discontinuity of their individual myonemes; polykinety comprises three peniculi, each consisting of three kineties. The high infestation showed here could be related to the preference for eutrophic environments showed by C. polypinum and suggested that ciliate epibionts may be ecologically important in aquatic habitats.

In samples of raw sewage collected from a sewage treatment plant in Rio de Janeiro (ETE-Penha), we found populations of two species, Deviata estevesi Paiva & Silva-Neto, 2005 and Deviata brasiliensis sp. nov. The organisms were studied in vivo under phase contrast microscopy, differential interference contrast (DIC), and after protargol-impregnation. The population of D. estevesi exhibited more extensive variation in cirral pattern than previously described. The interphasic organisms of new species D. brasiliensis sp. nov. are distinguishable from their congeners based on a series of morphometric features: cirral row R3 usually presents 1-3 cirri behind the right frontal cirrus, on average there are four macronuclear nodules, and, during morphogenesis of cell division, primordium V of the proter originates from the anterior region of cirral row R5 instead of row R6, as in the type species D. abbrevescens Eigner, 1995. In D. estevesi, the ventral cirral rows replicate by within-row primordia, which develop independently for the proter and for the opisthe, suggesting that it belongs to or is closely related to Parastrongylidium, hence the combination P. estevesi comb. nov. is established.