Vorticella protozoan. Differential interference contrast (DIC) light micrograph of a Vorticella sp. ciliate protozoan. This single-celled organism consists of a bell-shaped head, and a stalk that is anchored to the substrate (not shown). The stalk contains a contractile fibril called a myoneme. When stimulated this shortens, causing the stalk to coil like a spring (seen here). Magnification: x560 when printed at 10 centimetres wide.