Epistylis

Peritrichs are ciliated protozoans with bell-shaped cells attached to submerged objects by thread-like stalks. Stalks may be branched or solitary, sometimes contractile, depending on the species. Under certain conditions, peritrich populations become extremely dense, covering all available surfaces and growing even on fish and crustaceans. Tiny detached fibers can clog screens and filters in irrigation and other systems. Peritrichs thrive in nutrient-rich waters, where they feed mainly on bacteria.

Common genera include:

• Epistylis: Cells on branching, noncontractile stalks.
• Opercularia: Similar to Epistylis, but with a central protrusion from the apex of the cell.
• Carchesium: Cells on branching stalks. Each cell can contract slightly, independent of the others.
• Vorticella: Cells on unbranched stalks. Each stalk contains a helical fiber which, upon contracting, throws the stalk into a tight coil.
• Zoothamnium: Branching stalk with a single contractile element, so the entire colony contracts at once.