Vorticella is a genus of protozoa, with over 16 known species. They are stalked, inverted bell-shaped ciliates, placed among the peritrichs. Each cell has a separate stalk anchored onto the substrate, which contains a contractile fibril called a myoneme. When stimulated, this shortens, causing the stalk to coil like a spring. Vorticella species mainly live in freshwater ponds and streams—generally anywhere protists are plentiful. Other genera, such as Carchesium, resemble Vorticella, but are branched or colonial.