Apicomplexa: Eimeriidae) obtained from rheas, Rhea americana, is reported in Brazil. Oocysts of Isospora rheae sp. nov. are spherical to subspheroidal, measuring 22.6 × 21.0 µm, and have a double and smooth wall that is approximately 1.7 µm thick. The micropyle, oocyst residuum and polar granule are absent. Sporocysts are slightly ovoid, measuring 13.9 × 9.6 µm. The Stieda body is flattened, the substieda body is pointed, irregular and wavy and the sporocyst residuum is composed of scattered granules of varying sizes. Sporozoites have an oblong refractile body and one nucleus. This is the first description of an isosporid coccidian infecting birds of the family Rheidae.
Keywords: Coccidian; Isospora; Morphology; Morphometry; Oocysts; Ratite.