Euglena is a well-known genus of
flagellate protozoa, typical of the
euglenids, and commonly found in nutrient-rich freshwater, with a few marine species. The cells vary in length fom around 20 to 300 μm, and are typically cylindrical, oval, or spindle-shaped, with many bright green
chloroplasts and a single emergent
flagellum.
Euglena was first named by
Ehrenberg in 1830, and since then over 100 species have been described. The name comes from the Greek words
eu and
glêne, or
good eye, referring to the light-sensitive eyespot.
Genetic studies suggest that the genus Euglena is paraphyletic to various other uniflagellate euglenids. Most species fall into two major lineages: those which exhibit metaboly, including colourless species normally treated as Astasia and Khawkinea, and those with more rigid pellicles, including some normally included in Lepocinclis. As such, it is likely that the genus will be redefined in future classifications.
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