A new species of Eimeria Schneider, 1875 (Apicomplexa: Eimeriidae) from the dusky rice rat Melanomys caliginosus (Tomes) (Mammalia: Rodentia) in Costa Rica

We collected faecal samples from 24 dusky rice rats, Melanomys caliginosus (Tomes) (Rodentia: Cricetidae: Sigmodontinae), in a Biological Reserve in Costa Rica, and found three (12.5%) to be infected with a species of Eimeria Schneider, 1875, which we describe here as new. Sporulated oocysts of Eimeria caliginosa n. sp. are almost spheroidal and measure 16-21 x 17-20 (mean 19.6 x 18.2) mu m; micropyle, oocyst residuum and polar granule are absent. Sporocysts are ovoidal, 9-13 x 6-8 (mean 11.2 x 6.7) mu m, with small Stieda and sub-Stieda bodies present, but a para-Stieda body is absent; the sporocyst residuum is a compact mass of c.11-15 granules, c.5 mu m wide. Sporozoites are crescent-shaped, 5-8 x 2-3 (mean 6.8 x 2.4) mu m. This is the third species of Eimeria described from the genus Melanomys Thomas.