A new species of Caryospora (Apicomplexa: Eimeriidae) from the flathead snake, Tantilla gracilis (Ophidia: Colubridae), in southeastern Oklahoma.

A single flathead snake, Tantilla gracilis , collected in early October 2010 from Choctaw County, Oklahoma, was found to harbor an undescribed species of Caryospora . Oocysts of Caryospora choctawensis n. sp. were spherical to subspherical, 15.8 × 15.0 (14-18 × 14-16) µm, with a thick, bilayered wall and a shape index (length∶width) of 1.1. A micropyle and an oocyst residuum were absent, but prominent Stieda and bubble-like sub-Stieda bodies were present as well as a bilobed polar granule near the oocyst wall. Sporocysts were ovoidal, 10.8 × 9.0 (10-12 × 8-9) µm, with a shape index of 1.2. The sporocyst residuum was spherical and composed of a cluster of granules often membrane-bound. This is the second time a caryosporan species has been reported from T. gracilis but the first coccidian ever described from a reptilian host in Oklahoma. Additional T. gracilis from Arkansas (n  =  6), Oklahoma (n  =  1), and Texas (n  =  7) were examined, and a single specimen from Newton County, Arkansas harbored Caryospora gracilis Upton, McAllister, Trauth, and Bibb, 1992 , previously reported from T. gracilis collected in Arkansas and Texas.