Stentor and batrachospermum algae. Polarised light micrograph of a section through a Stentor sp. ciliate protozoan (centre) amongst Batrachospermum sp. freshwater red algae. Stentors are freshwater protozoa that feed mainly on bacteria. They move by beating their cilia, hair-like extensions that cover their body. The small green bodies inside the protozoan are individual Zoochlorella sp. algae, which have a symbiotic relationship with the protozoan. They photosynthesise inside the Stentor, providing it with sugars and oxygen, while deriving protection from their host. Magnification: x140 when printed 10 centimetres wide.