A new species of (Apicomplexa: Eimeriidae) from the yellow warbler, (L.) (Passeriformes: Parulidae: Parulinae), in Oklahoma, USA.

n. sp. is described from a yellow warbler, (L.), from McCurtain County, Oklahoma, USA. Oöcysts of the new species are subspheroidal to ovoidal with a smooth bi-layered wall, measure (L × W) 24.2 × 20.4 μm, and have a length/width (L/W) ratio of 1.2; a micropyle and oöcyst residuum are both absent, but polar granule(s) are present. Sporocysts are ovoidal to ellipsoidal and measure 14.5 × 9.2 μm, L/W ratio of 1.6; a knob-like Stieda body is present as well as a distinct rounded sub-Stieda body. The sporocyst residuum is composed of various-sized granules in a compact rounded or irregular mass or dispersed between and across the sporozoite. The oöcysts of n. sp. can be differentiated from five other congeners reported from members of the New World warbler family Parulidae from either Mexico, Costa Rica, or Brazil, by being larger on average as well as by possessing a prominent rounded sub-Stieda body, sporozoite striations, and an posterior refractile body. Information is also presented on an sp. being passed by that we choose not to describe as a putative novel species of at this time. These two isosporans represent the first coccidians reported from and, more importantly, the first known from the members of the Parulidae in the USA.