Morphological characteristics of Sarcocystis bertrami sarcocysts isolated from the skeletal muscle of a horse. (A) Sarcocyst (unstained, light microscopy) bound by villar protrusions (vps). Scale bar = 10 μm. (B) Longitudinal section of a sarcocyst (under transmission electron microscopy, TEM). The sarcocyst is surrounded by the host cell (hc), and the sarcocyst wall exhibits numerous vps, which are often bent along the cyst surface. The vps contain bundled microtubules (mt) in the core, which penetrate diagonally into the ground substance (gs). Scale bar = 1 μm. (C) Cross-section of a sarcocyst under TEM. Note the bundle of mt in the gs. Scale bar = 1 μm.