This scanning electron micrograph (SEM) depicted the mucosal surface of the small intestine of a gerbil infested with Giardia sp. protozoa. The intestinal epithelial surface is almost entirely obscured by the attached Giardia trophozoites. The protozoan Giardia causes the diarrheal disease called giardiasis. Giardia species exist as free-swimming (by means of flagella) trophozoites, and as egg-shaped cysts. It is the cystic stage, which facilitates the survival of these organisms under hars