Stentor polymorphus. Light microscopy footage of the ciliate protozoan green stentor (Stentor polymorphus). This freshwater protozoan feeds mainly on bacteria. Its green colour is caused by the presence of numerous individual Zoochlorella algae, with which it has a symbiotic relationship. The algae photosynthesise inside the protozoan, providing it with sugars and oxygen, while deriving protection from their host. Filmed with darkfield illumination.