Chris T. McAllister, John A. Hnida, Eric Leis
During August 2025, a single adult yellow-bellied watersnake, Nerodia erythrogaster transversa was found dead on the road in Montgomery County, Arkansas, USA, salvaged, and its feces examined for coccidian parasites. Fecal material from the rectum was placed in a vial of 2.5% potassium dichromate and examined by light microscopy. Partially sporulated oocysts were initially found and allowed to completely sporulate. The snake was found to be passing a new species of Eimeria. Oocysts of Eimeria speairsi sp. n. were ovoidal to spheroidal with a slightly rough bi-layered wall, measured (L × W) 28.0 × 18.2 µm, and had a length/width (L/W) ratio of 1.5; a micropyle, oocyst residuum, and polar granule was absent. Sporocysts are ellipsoidal and measured 13.7 × 8.6 µm, L/W ratio of 1.6; a flattened Stieda body was present but sub-Stieda and para-Stieda bodies were absent. The sporocyst residuum was composed of various-sized granules in a compact rounded or irregular mass, sometimes dispersed between the sporozoites. A 412 bp sequence of the SSU rRNA gene produced for E. speairsi sp. n. showed a relatively low level of similarity. The species description is based primarily on oocyst morphology and partial SSU rRNA sequence data from the single host snake. In addition, an updated summary of the coccidians of North American watersnakes is provided.