Protozoan algae. Light micrograph of Euglena acus, a protozoan algae. The internal components of this single-celled creature can be seen, as can the hair-like flagellum (at right) that it uses to propel itself through the water. These flagellates are the most primitive type of protozoa. E. acus produces its food from light by photosynthesis. Its green color is caused by the presence of chlorophyll, a chemical needed for photosynthesis. Euglena sp. protozoa can reach such numbers that they can make the water appear green. Magnification: x300 at 35mm size.