Proto-Sumubulum were found 113 million years ago by the Glavers on a large, rocky world orbiting a chain of small, brown dwarf suns. Their homeworlds was wracked by pertuberations from an irregular orbit and ovoid. Life had retreated to a few algae pools smaller than the Great Lakes of Earth. The Sumubulum normally are seen wearing anti-G encounter suits.

Since a long time the Sumubulum have retired from all major Institutes, becoming more enigmatic, living on a series of Coal Sack worlds. They earn a living by offering translation and mediation services between oxygen-breathing and hydrogen-breathing races.

Sources: Contacting Aliens, An Illustrated Guide to David Brin's Uplift Universe