Paramecium protozoan. Light micrograph of Paramecium caudatum, a ciliate protozoan (at centre right). The protozoan has ejected thread- like trichocysts. These are produced by the creature when touched or exposed to certain chemicals. It is believed that they act as a defence mechanism or are used to anchor P. caudatum to stationary objects, although their exact function remains a mystery. P. caudatum propels itself by beating tiny, hair-like structures (cilia) which project from its body. The protozoan lives in stagnant water, feeding on bacteria and plant particles. Magnification: x133 at 35mm size.