Paramecium protozoan. Coloured scanning electron micrograph (SEM) of a Paramecium sp. ciliate protozoan. Its single cell is covered in numerous cilia, hair-like structures that it beats for propulsion, and to waft food particles into its mouth (not seen). Paramecium sp. protozoa inhabit fresh water, and feed mainly on bacteria and smaller protozoa. There are many species of Paramecium, which vary in size from under 100 micrometres (millionths of a metre) to over 300 micrometres in length.