Differential interference contrast (DIC) light micrograph of Paramecium sp. Paramecium is a ciliate protozoan, with oral groove, food vacuoles, nucleus, and cilia. Paramecium are found mainly in stagnant ponds, feeding on bacteria and plant particles. They have a permanent mouth called an oral grove. Food taken in through the oral groove is digested within temporary digestive vacuoles in the cell cytoplasm. The two contractile vacuoles act as osmotic regulators, controlling the flow of water across the ciliate's membrane. The contractile vacuoles are surrounded by a halo of radiating channels. Excess water collects in the channels, drains into the vacuole and is then discharged through a pore at the surface. Magnification: x240 when printed at 10 centimetres wide at its longest edge.