The Quelin are a species that is part of the Galactic Commons. They are said to be there so Harmagians can gain access to their vast natural resources.

Rosemary describes the Quelin as "lobster centaurs". They are a blue arthropodic species with many legs, mask-like faces, and flat, black eyes. They have thick, black-blue domes on the top of their head they can use as rams. They often decorate their shells with symbols and polished stones. Although they are a part of the Galactic Commons, it is rare for a Quelin to travel outside of their own space, as they are a particularly xenophobic species.

Quelin are often a harsh and bureaucratic species. They have strict laws against inter-species relationships and cloning. Cloning is seen as especially evil because of a series of Quelin wars involving eugenics and cloning. Artis Corbin, a crew member on the Wayfarer, was discovered to be a clone and was treated violently while a prisoner of the Quelins. Teracite ore, used to create circuit panels and other tech on ships, is mined in penal colonies by Quelin prisoners.