Blepharisma ciliate protozoan. Coloured scanning electron micrograph (SEM) of a ciliate protozoan (Blepharisma sp.). This tiny single- celled organism is found in freshwater. It feeds on bacteria and decaying organic matter, which it filters through membranelles in its primitive mouth, known as a buccal cavity (bottom). The membranelles, rows of fused cilia (short microscopic hairs), are also used for locomotion. When feeding conditions are good this protozoan can grow to an enormous size and the giant Bleparisma is sometimes seen to feed on its normal sized relatives.