The number and shape of chloroplasts within "Euglena" varies greatly. "Euglena" are able to move through aquatic environments by using a large flagellum for locomotion. To detect light, the cell has an eyespot, a primitive organelle that filters sunlight into light-detecting, photo-sensitive structures. These structures, at the base of the flagellum, allow only certain wavelengths of light to register. With the aid of this photo-sensitive area, the "Euglena" can shift its position to get better photosynthesis. 