Stentor coeruleus (pronunciationⓘ[a]) is a protist in the family Stentoridae which is characterized by being a very large ciliate that measures 0.5 to 2 millimetres when fully extended.

S. coeruleus specifically appears as a very large trumpet.

[3] When this organism is cut in half, each half is able to regenerate a cell that has its normal anatomy provided that each cut part includes some of the macro-nucleus.

[4] It feeds by means of cilia that carry food into the gullet.

[5] S. coeruleus is capable of sexual reproduction, or conjugation, but primarily reproduces asexually by binary fission.