A New Eimerian (Apicomplexa: Eimeriidae) from the Barn Swallow, (Aves: Passeriformes: Hirundinidae), in Southeastern Oklahoma: The Fourth Eimerian Species from New World Passeriformes.

Barn swallows () are the most widespread swallow species in the world. However, little is known about the coccidian parasites of . Feces from a single nesting in McCurtain County, Oklahoma, were collected in May 2018 and examined for coccidia; the swallow was found to be passing a new species of . Oocysts of n. sp. are ellipsoidal with a smooth bi-layered wall, measure (L × W) 25.5 × 15.2 μm, and have a length/width (L/W) ratio of 1.7; a micropyle and oocyst residuum are absent, but polar granule(s) are present. Sporocysts are ellipsoidal and measure 12.8 × 6.5 μm, L/W 2.0; a nipple-like Stieda body is present, but sub-Stieda bodies and para-Stieda bodies are absent. The sporocyst residuum is composed of a compact spheroid with a dense, irregular mass of finer granules lying between and dispersed among the sporozoites. This is the first eimerian reported from and the family Hirundinidae, and only the fourth spp. known from passerine birds of the New World.