Euglena

Euglena are unicellular organisms that belong to the genus protist. As such, they are not plants, animals or fungi. In particular, they share some characteristics of both plants and animals. While they can manufacture their own food, a characteristic seen in plants, they are also capable of movement and consuming food, which are characteristics of animals. Due to their unique characteristics, there has been some debate as to the phylum in which Euglena should be placed. Historically they have been classified by scientists in either the phylum Euglenozoa or the phylum Euglenophyta. Euglenoids organized in the phylum Euglenophyta were grouped with algae because of the many chloroplasts within their cells. But Since other Euglena do not have chloroplasts and the ones that do! obtained them through endosymbiosis, some scientists contend that they should be placed taxonomically in the phylum Euglenozoa. Euglena live in fresh and brackish water rich in organic matter and can also be found in moist soils. Euglena are characterized by an elongated cell with one nucleus, numerous chlorophyll-containing chloroplasts, a contractile vacuole, 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, Euglena lack a rigid cellulose wall and have a flexible pellicle that allows them to change shape. Though they are photosynthetic, most species can also feed heterotrophically and absorb food directly through the cell surface via phagocytosis. Food is often stored as a specialized complex carbohydrate known as paramylon, which enables the organisms to survive in low-light conditions. Most Euglena have a life cycle consisting of a free-swimming stage and a non-motile stage. In the free-swimming stage, Euglena reproduce rapidly by a type of asexual reproduction method known as binary fission. The euglenoid cell reproduces its organelles by mitosis and then splits longitudinally into two daughter cells. When environmental conditions become unfavorable and too difficult for Euglena to survive, they can enclose themselves within a thick-walled protective cyst. Protective cyst formation is characteristic of the non-motile stage.