The trophozoite of Balantidium coli lives in the intestine of mammals. It can be identified as a ciliate by the presence of cilia and of a macronucleus and micronucleus. The tiny micronucleus is often hidden by the large macronucleus.
This photo clearly shows the distinctive, dumb-bell shaped macronucleus. A food vacuole is visible above and to the right of the macronucleus.