Euglena Ehrenberg
	From Greek eu, "good, true, primitive" + gleen, "eye"
Metaboly movements of Euglena.	Euglena is a photosynthetic euglenoid with at least 150 described species. The cells are cylindrical with a rounded anterior and tapered posterior. The chloroplasts are well-developed, bright green, and sometimes have pyrenoids. They are often discoidal in shape but can also be ovate, lobate, elongate, U-shaped, or ribbon-shaped. Some researchers use the structure and position of the chloroplasts to divide the group into three subgenera. Even though they are able to photosynthesize, Euglena cells also have a phagotrophic ingestion apparatus. Euglena has one long, protruding flagellum and a shorter flagellum that is not usually visible.   The euglenoids can glide and swim using their flagella, or can ooze along a substrate with an undulating, shape-changing, contraction motion called metaboly. The cytoplasm of Euglena and other euglenoids contains many paramylon starch storage granules. The euglenoid cells are covered by a pellicle composed of ribbonlike, woven strips of proteinaceous material that cover the cell in a helical arrangement from apex to posterior. Freshwater euglenoids have a contractile vacuole. Euglenoids sense light using a red pigmented eyespot or stigma and the paraflagellar body located at the base of the emergent flagella.
Some species of Euglena produce hematochrome pigments in response to changes in light levels. These cells can quickly change from green to red and back again in less than 10 minutes. The cell appears red when the hematochrome granules are dispersed throughout the cell and appears green when the granules are confined to the center of the cell and the chloroplasts are visible. A noticeable red slime can accumulate on water surfaces with high temperatures and abundant dissolved organics.