Isospora dipperia n. sp. (Apicomplexa: Eimeriidae) from the American dipper Cinclus mexicanus Swainson (Passeriformes: Cinclidae) in Yosemite National Park, USA.

Isospora dipperia n. sp. is described from the feces of the American dipper Cinclus mexicanus Swainson collected in Yosemite National Park, California, USA. Sporulated oöcysts of the new species are subespherical, 20-24 × 17-21 (20.9 × 18.7) μm, with a length/width (L/W) ratio of 1.0-1.1 (1.1); one polar granule is present, but micropyle is absent. Sporocyts are lemon-shaped, 14-16 × 8-11 (15.5 × 9.8) μm, with a L/W ratio of 1.6; prominent Stieda and sub-Stieda bodies are both present, but para-Stieda body is absent. Sporocyst residuum of many scattered granules is present and the sporozoites have prominent anterior and posterior refractile bodies. The mean dimensions (15.9 × 13.8 µm) of unsporulated oöcysts of I. cincli Gottschalk, 1972 from the white-throated dipper C. cinclus (L.) in Europe, appear to be considerably smaller than those in I. dipperia n. sp. Comparisons of Isospora dipperia n. sp. with two species of Isospora Schneider, 1881 described in the Americas from birds of the family Sturnidae, related to Cinclidae, revealed that the mean dimensions of the sporulated oöcysts in the new species are considerably smaller than those in I. graculai Bhatia, Chauhan, Arora & Agrawal, 1973 from Gracula religiosa (24.6 × 22.4 µm) and I. rothschildi Upton, Wilson, Norton & Greiner, 2001 from Leucopsar rothschildi (22.3 × 21.6 µm). The new species is the first species of Isospora recorded in a bird of the family Cinclidae in the New World.