"Balantidium coli trophozoites.  These are characterized by:

• Their large size (40 µm to more than 70 µm)

• The presence of cilia on the cell surface - particularly visible in (B)

• A cytostome (arrows)

• A bean shaped macronucleus which is often visible - see (A), and a smaller, less conspicuous micronucleus"

• Courtesy of the Division of Parasitic Diseases at the National Center for Infectious Diseases, Centers for Disease Control and Prevention