A new coccidian parasite (Apicomplexa: Eimeriidae: Eimeria) from the southern black racer, Coluber constrictor priapus (Reptilia: Ophidia: Colubridae) from Arkansas, USA.

Between April 2012 and October 2017, 18 southern black racers, Coluber constrictor priapus, were collected from nine counties of Arkansas (n = 13) and McCurtain County, Oklahoma (n = 5) and their faeces examined for coccidian parasites. One of 18 (6%) C. c. priapus harboured an eimerian that we describe here as new. Oocysts of Eimeria dunni sp. nov. were subspheroidal with a lightly pitted bi-layered wall measuring L × W 24.0 × 21.1 and L/W ratio of 1.2. A micropyle was absent but an oocyst residuum and polar granule were present. Sporocysts were ovoidal and measured 11.9 × 8.1 with L/W of 1.5. A Stieda body was present but substieda and parastieda bodies were absent. The sporocyst residuum was composed of medium-sized granules aligned along perimeter of sporocyst or in a dispersed mass. This represents the first valid eimerian reported from the southern black racer.