EN
A species of Sarcocystis is reported from two naturally infected Buffon’s macaws (Ara ambigua) from Costa Rica. Only mature sarcocysts, measuring up to 950 μm in length and up to 75 μm in width, were observed. By light microscopy the sarcocyst wall was thin (< 1 μm thick) and smooth. The villar protrusions on the sarcocyst wall were up to 4.0 μm long and up to 0.6 μm wide; they were folded over the sarcocyst wall giving a thin-walled appearance. The microtubules in villar protrusions were smooth and confined to villar protrusions. Bradyzoites in sections were 4.0–5.9 × 0.8–1.8 μm in size. Structurally, sarcocysts from the macaw appeared different from sarcocysts of other avian species. This is the first report of Sarcocystis infection in this host.