A new species of Eimeria Schneider, 1885 (Apicomplexa: Eimeriidae) from Harris's antelope squirrel Ammospermophilus harrisii Audubon & Bachman (Rodentia: Sciuridae).

Eimeria ammospermophili n. sp. (Apicomplexa: Eimeriidae) is described from 2 of 29 (7%) Harris's antelope squirrels Ammospermophilus harrisii Audubon & Bachman in Arizona, USA. Sporulated oöcysts of this new species are ovoidal to ellipsoidal, 24-32 × 20-25 (29.0 × 22.7) µm, with a pitted, bi-layered wall, an oöcyst residuum and, occasionally, a polar granule. Sporocysts are ellipsoidal, 10-12 × 7-9 (11.0 × 7.9) µm, with a Stieda body and sporocyst residuum; sporozoites are elongate with a spheroidal anterior refractile body and an ellipsoidal posterior refractile body. In addition, sporulated oöcysts of Eimeria vilasi Dorney, 1962 are described from A. harrisii. This is the first report on the coccidia of this host species.