According to Kenyon College, the structure of the single-celled eukaryotic Euglena includes a spiral exoskeleton outside of a long, thin cell with a flagellum for motion and, in most cases, several internal chloroplasts. They are capable of both photosynthesis and consuming other organisms in their environment.
Kenyon College explains that Euglena cells are among the simplest cells with nuclei. They can survive as heterotrophs in dark environments, but obtain chloroplasts and conduct photosynthesis in the presence of light. Euglena cells do this by absorbing algae and exchanging genes between themselves and the enveloped organisms. Despite their simplicity, they possess many of the basic organelles of other eukaryotic cells.