Two new Eimeria spp. (Apicomplexa: Eimeriidae) from the dusky rice rat, Melanomys caliginosus, Tome 1860, in Costa Rica.

We collected fecal samples from 9 dusky rice rats, Melanomys caliginosus (Rodentia, Cricetidae, Sigmodontinae), in a Biological Reserve in Costa Rica and found 8 (89%) to be infected with 2 Eimeria species which we describe here as new. Sporulated oocysts (n = 20) of the first, Eimeria melanomytis n. sp., are cylindroidal and measure 20.1 × 13.3 μm (18-23 × 13-15); micropyle and oocyst residuum are both absent, but a bilobular polar granule is present. Its sporocysts are ovoidal, 10.5 × 7.4 μm (10-13 × 6-8) with a small Stieda body, but both substieda and parastieda bodies are absent; a spheroidal sporocyst residuum is present, ≈ 5 μm wide. Sporulated oocysts (n = 20) of the second, Eimeria rebambensis n. sp., are subspheroidal, 21.2 × 17.0 μm (19-23 × 14-18); micropyle and oocyst residuum are both absent, but with a polar granule ≈ 2 μm wide. Sporocysts are elongate-ovoidal, 12.4 × 7.0 μm (11-14 × 6-9) with a distinct knob-like Stieda body, and a substieda body directly beneath it which is about twice as wide, but no parastieda body is present; the sporocyst residuum is an irregular mass composed of 8-10 globules scattered among the sporozoites, which are ≈ 10 × 5 μm, and have 1 refractile body at their wider end and a central nucleus. These are the first eimerians described from this rodent genus.