Vorticella. Light microscope footage of two Vorticella sp. ciliate protozoa. 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 food in the water.