(spa-thid-ee-um), a predatory ciliate. the mouth is the slightly expanded region at the front (top) of the cell and this is underlain with extrusomes which assist in the capture of food. The structure at the back end is the contractile vacuole. These guys usually eat other ciliates. Differential interference contrast. Material from Nymph Creek and Nymph Lake, thermal sites within Yellowstone National Park, photograph by Kathy Sheehan and David Patterson.