Ophrydium and heliozoan protozoa. Polarised light micrograph of a group of Ophrydium sp. Protozoa (long) with a single heliozoan (round). Ophrydium are colonial micro-organisms that contain green algae (green) inside their bodies. The algae has a symbiotic relationship with the protozoa. It photosynthesises inside the protozoan's body providing it with sugars and oxygen, while deriving protection from their host. Magnification: x100, when printed 10 centimetres wide.