Stentor coeruleus is a protist of the Stentor genus. It belongs to the Stentoridae family which is characterized by being a very large ciliate that measures 0.5 to 2 millimetres when fully extended. Stentor coeruleus specifically appears as a very large trumpet. It contains a macronucleus that looks like a string of beads that are contained within a ciliate that is blue to blue-green in color. Being that it has many myonemes, it has the ability to contract into a ball. It has the ability to swim while both fully extended or contracted.