Protozoa were simple microorganisms comprised of a single cell. There were many variations of protozoa – for example, some moved through the act of flagellation, and some contained no nuclei. (VOY: "Message in a Bottle") The space-dwelling lifeforms encountered by the USS Voyager in 2371 reminded Captain Kathryn Janeway of protozoa due to the way they propelled themselves through space. (VOY: "Elogium")