Scanning Electron Micrograph (SEM) showing Giardia muris protozoan settled atop intestinal mucosal villi, adhering itself to the microvillous border of intestinal epithelial cells. Each small circular profile under the protozoan represents the rounded tip of a single microvillous, and it is estimated that 2000 to 3000 microvilli cover the surface of a single intestinal epithelial cell. The protozoan Giardia causes the diarrheal disease called giardiasis.