Euglena Gracilis Single Celled Organism Microscopic Scene

Euglena as seen under my microscope from a larger field view and then close up as it slides around in a drop of water swinging its flagellum out in front.

Euglena is a genus of unicellular flagellate protists. It is the best known and most widely studied member of the phylum Euglenozoa (also known as Euglenophyta), a diverse group containing some 44 genera and at least 800 species. Species of Euglena are found in fresh and salt waters. They are often abundant in quiet, inland waters, where they may bloom in numbers sufficient to color the surface of ponds and ditches green (E. viridis) or red (E. sanguinea).

The species Euglena gracilis, has been used extensively in the laboratory as a model organism.

Most species of Euglena have photosynthesizing chloroplasts within the body of the cell, which enable them to feed by autotrophy, like plants. However, they can also take nourishment heterotrophically, like animals. Since Euglena have features of both animals and plants, early taxonomists, working within the Linnaean two-kingdom system of biological classification, found them difficult to classify. Indeed, it was the question of where to put such "unclassifiable" creatures that prompted Ernst Haeckel to add a third kingdom to the Animale and Vegetabile of Linnaeus: the Kingdom Protista.