Stentor, sometimes called trumpet animalcules, are a genus of filter-feeding, heterotrophic ciliates, representative of the heterotrichs.

[1] The body, or cortex, is generally horn-shaped, hence the association with the Greek herald, and the former name "trumpet animalcule".

A ring of prominent cilia around the anterior "bell" sweep in food and aid in swimming.

Stentor can come in different colors: for example, S. coeruleus can appear blue due to the presence of stentorin, a natural pigment.

Because the concentration of salt inside the cell and in the surrounding freshwater is different, Stentor must store water that enters it by osmosis and then discharge it from the vacuole.