Trill Symbiont

The Trill Symbiont is a sentient vermiform lifeform from the planet Trillius Prime. It is transferred from one humanoid Trill host to another upon the death of the host. The Symbiont takes with it all memories of the previous Trill hosts. Upon joining, the new Trill host will gain these memories. The Symbionts live in Caves of Mak'ala on Trillius and are cared for by the Guardians. They communicate with each other via electrical impulses transmitted through the milky water they live in.

Also See

Memory Alpha