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 covering of cilia that are used for locomotion. The macronucleus is out of focus but is surrounded by three food vacuoles. The gullet can be seen at the 11 o'clock position.