Vorticella protozoa. Differential interference contrast (DIC) light micrograph of Vorticella sp. ciliate protozoa. Vorticella are sessile, meaning they attach to a surface and cannot move around on their own. When disturbed, they contract their stalk into a tight coil. This contraction is one of the fastest known actions in the animal kingdom. Magnification: x286 when printed 10 centimetres wide.