Stentor polymorphus. Light microscope footage of two green stentor (Stentor polymorphus). This species of freshwater ciliate protozoan feeds mainly on bacteria. Its green colour is caused by the presence of numerous individual Zoochlorella sp. 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.