A neural parasite is a type of lifeform that derives sustenance from the brain or mental energy of another lifeform, or simply uses that lifeform as a host in order to propagate a life-cycle of parasitic behavior. Notable neural parasites include the blastoneurons that spread to Deneva 2267 and the bluegill parasites that attempted to take over Starfleet in 2364. (TOS episode & Star Trek 2 novelization: Operation -- Annihilate!; TNG episode: "Conspiracy")