File:Giardia muris trophozoite SEM 11643.jpg

English: This scanning electron micrograph (SEM) clearly showed the ventral surface of a Giardia muris trophozoite. The ventral adhesive disk resembles a suction cup, where overlapping microtubules in the cytoplasm form a number-6-shaped figure. Giardia muris has four pairs of flagella that are responsible for the organism’s motility. The adhesive disk facilitates adherence of the protozoan to the intestinal surface. 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 harsh environmental conditions. The cyst is considered the infective form, and disease is often transmitted by drinking contaminated water. As depicted in these SEMs, in the intestine, cysts are stimulated to liberate trophozoites. Cysts can be shed in fecal material, and can, thereafter, remain viable for several months in appropriate environmental conditions. Cysts can also be transferred directly from person-to-person, as a result of poor hygiene.