Light microscopy of a Vorticella sp. protozoan. Vorticella are stalked, inverted bell_shaped ciliates. 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. They feed by wafting tiny food particles into their mouths with the cilia around the bell.