ABSTRACTFeces from a juvenile specimen of the anteaterTamandua tetradactylafrom Ponta de Pedras, Marajó, Pará, northern Brazil, contained three different coccidial oocysts:Eimeria tamanduaeLainson, 1968;E. corticulataLainson&Shaw, 1990; and a third species previously unrecorded and described here asEimeria marajoensisn. sp. Oocysts of the latter parasite are spherical to subspherical, 13.9 ± 1.5 times 13.4 ± 1.4 (11.1‐16.5 times 11.1‐16.5) μm, shape index (length/width) 1.0 (1.0‐1.2). the oocyst wall is a single, Colorless layer about 0.6‐1.0 μm thick with no striations or micropyle. There is no oocyst residuum, but a single, round, oval or irregularly shaped polar granule of about 0.75‐2.5 μm is consistently present. the sporocysts are broadly ellipsoidal, 7.1 ± 0.7 ± 5.3 ± 0.6 (6.0‐8.8 times 4.0‐5.7) μm, shape index 1.3 (1.2‐1.5), with a delicate wall bearing a minute stieda body. No sub‐stieda body was visible. the sporocyst residuum consists of some 10‐20 rounded granules, lying between the two slightly curved sporozoites which measure approximately 6.5 times 2.0 μm. Sporocyst refract