Ophrydium protozoa. Darkfield illuminated polarised light micrograph of a group of Ophrydium sp. Protozoa. These colonial micro-organisms contain green algae (green) inside their bodies, which 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: x400, when printed 10 centimetres wide.