Trill

Trill refers to two species from the planet Trill: one is humanoid and distinguished by a pattern of spots on the legs up to the head, and the other is a parasitic slug-like organism called a symbiont. The symbionts will often "join" with a humanoid host so they can experience the universe at large.

The Trill mathemetical system is noted for containing ethical modes. (novel: Intellivore)