Elysium parasite

The Elysium parasites, as called by Ace, were a species of cosmic parasites that, were they not restricted by their metabolism, could have overrun the universe. They referred to themselves as "Life," distinguishing between "Life" and "life."

The only known specimen was the Artifact located in the Elysium system. It contained an entire ecosystem within itself, and extended into more than eleven dimension, even containing portals akin to singularities. Their eggs were the size of planets and were laid in gas giants, taking hundreds of years to mature and hatch. When he became psychically linked to the Artifact, the Seventh Doctor was able to make it so that all future offspring would be symbiotes rather than parasites. (PROSE: Parasite)