Vorticella protozoan. Coloured scanning electron micrograph (SEM) 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. The stalk contains a contractile fibril called a myoneme. When stimulated this shortens, causing the stalk to coil like a spring (seen here). Magnification: x1300 when printed at 10 centimetres wide.