In biology, Stentor is a genus of ciliate protozoa, representative of the heterotrichs. The body is generally trumpet-shaped, hence the association with the herald, with a ring of prominent membranelles around the anterior "bell" that sweep in food and aid in swimming. Stentor are common in freshwater lakes and streams, usually attached to algae and other detritus. Some reach several millimetres in length, making them among the largest single-celled organisms.