First report of Tyzzeria parvula (Kotlán, 1933) Klimes, 1963 (Apicomplexa: Eimeriidae), in swan goose Anser cygnoides L., 1758, in Brazil.

This is the first description of Tyzzeria parvula from the swan goose (Anser cygnoides) in the State of Rio de Janeiro, Brazil. Fecal samples were collected from 15 swan geese, but only four of them shed oocysts in feces. After sporulation, the oocysts were spherical to sub-spherical, and measured 12.4 +/- 1.0 (11-15) x 10.4 +/- 0.8 mum (8-12). They presented a shape index of 1.2 (1.0-1.4), with a bi-layered wall that was 0.7 +/- 0.1 mum (0.6-0.8) thick. The outer side was smooth and colorless, while the inner side was pale greenish. Micropyles and polar granules were absent. The residuum sometimes formed a mass of spherules and granules and, at other times, was dispersed. Sporozoites had one rounded end and the other end was fine and slightly curved.