Dark field light micrograph of a colony of Ophrydium sp. protozoa with Pediastrum duplex and diatoms inside. Ophrydium contain green algae inside their bodies that have a symbiotic relationship with the protozoa. They photosynthesise inside the protozoan's body providing it with sugars and oxygen, while deriving protection from their host. Magnification: x186 when printed 10 cm wide.