any of a genus (Euglena) of green protists with a single flagellum, a reddish eyespot, and a flexible body shape
See euglena in American Heritage Dictionary 4
(yo͞o-glēˈnə)
noun
Any of various minute single-celled freshwater organisms of the genus Euglena, characterized by the presence of chlorophyll, a reddish eyespot, and a single anterior flagellum.