Members of the genus Euglena have bodies made up of only one cell, making them unicellular. They are so small that a microscope is necessary to see them. In constrast, multicellular means an organism is made up of more than one cell.
Euglena are green in color because of the green algae that they consume, which they use to make food. Each Euglena has a long hair-like flagellum that stretches from its body. The flagellum is used to swim. In order to reproduce, the Euglena completes a process called mitosis, during which the organism splits in half to become two complete and separate organisms.