Stentor muelleri also called a trumpet ciliate is a protozoan (single-celled) organism which feeds on algae. It has a horned-shaped body and is usually 0.5–1.0 millimetre (0.02–0.04 in) long (exceptionally up to 3 mm or 0.12 in) and is found in freshwater bodies of water and sometimes estuaries. Stentor muelleri is a heterotrich.