The cyst stage of Giardia spp. transmits the parasite from host to host, via water, and provides sufficient protection that the parasite may survive for several weeks or longer.
This photo shows several features of a typical cyst. The outer cyst wall is thin and clear. Inside, a trophozoite has begun to divide, but will not complete division until ingested by a new host. Two of the sucking disks and nuclei are clearly visible at the bottom of the cyst; the other set is out of focus. Axostyles run from the pair of sucking disks up and to the right. The dark bars at the top of the cyst are the parabasal bodies.