Euglena, ![Euglena [Credit: Walter Dawn]](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_uLuT9rOqzy2OScrAYrlrmGzA5D5vwwn2JNeymta-5nDBjCozB0sqTJkrLGnL5ehUebMZUKRc2UOySicmq0nTKIlW1IUoPS6sRo5NlcRAK9YzWBwmgVkT5JUNvjutDrWN9EWteC1W8f=s0-d)
genus of more than 1,000 species of single-celled flagellated(i.e., having a whiplike appendage) microorganisms that feature bothplant and animal characteristics. Found worldwide, Euglena live in fresh and brackish water rich in organic matter and can also be found in moistsoils. As photosynthetic protists, Euglena have a taxonomy that is somewhat contentious, and the genus is often placed either in the phylum Euglenozoa or the algal phylum Euglenophyta.
genus of more than 1,000 species of single-celled flagellated(i.e., having a whiplike appendage) microorganisms that feature bothplant and animal characteristics. Found worldwide, Euglena live in fresh and brackish water rich in organic matter and can also be found in moistsoils. As photosynthetic protists, Euglena have a taxonomy that is somewhat contentious, and the genus is often placed either in the phylum Euglenozoa or the algal phylum Euglenophyta.
Euglena are characterized by an elongated cell (15–500 micrometres [1 micrometre = 10−6 metre], or 0.0006–0.02 inch) with one nucleus, numerous chlorophyll-containingchloroplasts (cell organelles that are the site of photosynthesis), a contractile vacuole (organelle that regulates the cytoplasm), an eyespot, and one or two flagella. Certain species (e.g., E. rubra) appear red in sunlight because they contain a large amount of carotenoid pigments. Unlike plant cells, Euglenalack a rigid cellulose wall and have a flexible pellicle (envelope) that allows them to change shape. Though they are photosynthetic, most species can also feed heterotrophically (on other organisms) and absorb food directly through the cell surface via phagocytosis (in which the cell membrane entraps food particles in a vacuole for digestion). Food is often stored as a specialized complex carbohydrateknown as paramylon, which enables the organisms to survive in low-light conditions. Euglenareproduce asexually by means of longitudinal cell division, in which they divide down their length, and several species produce dormant cysts that can withstand drying.
Some species, especially E. viridis and E. sanguinea, can develop large toxic populations of green or red “blooms” in ponds or lakes with high nitrogen content. E. gracilis is common in laboratory demonstrations, and a number of species are used to study cell growth and metabolism in various environmental conditions.
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