Vorticella. Light microscope footage of numerous Vorticella sp. ciliate protozoans (white) attached to a green plant stalk. These filter-feeding freshwater protozoa each consists of a bell-shaped head and a contractile stalk that is anchored to the substrate. When disturbed, the stalk is contracted in a protective motion. Cilia (tiny hair-like structures) attached to the head are used to capture food and also for movement. Vorticella live in both marine and freshwater environments, and feed on microscopic algae, bacteria and other aquatic material.