Exogorth

The Exogorth, colloquially known as the space slug, was a gigantic species of toothed gastropod. They were silicon-based lifeforms that survived in the vacuum of space by making their homes in the caverns and craters of asteroids. They fed primarily on the minerals of asteroids, various stellar energy fields, and stellar energy emissions. However if these food sources were scarce they would feed on other sources that may come their way or take inheritance within them such as mynocks (another silicon-based lifeform), ships, and other unfortunate creatures that unknowingly passed into its mouth.
They often maintaining a pleasant ecosystem within their bodies and were relatively peaceful. They are extremely unique due to their ability to have their bodies become stable ecosystems that were home to countless species that peacefully co-existed. This meant event species that could not survive the vacuum of space could survive if they were inside a Exogorth with a livable ecosystem, that is until they required additional nutrition. The average adult space slug grew to about 10 meters in length; however, there had been instances of near-kilometer-long specimens.