Ceti Eels are small non-sapient creatures native to the deserts of planet Ceti Alpha V. According to Khan, the Ceti Eel is the last indigenous lifeform on the planet. Once a habitable M-class world, Ceti Alpha V had its climate brutally altered after the destruction of the nearby planet Ceti Alpha VI, which shifted Ceti Alpha V's orbit.
A Ceti Eel has its body protected by a thick exoskeleton. They incubate their larvae between the plates of their jointed carapace. As adults, they are free-living burrowing creatures that spend most of the time hidden under the desert's sands. The larvae, however, are parasitoids. Once the larva leaves the protection of its parent's carapace, it will crawl into the ear of a larger being and burrow into the brain, causing the host severe pain, which leads to insanity and eventually death. As a side effect, it also makes the host extremely susceptible to suggestion.
- Star Trek II: The Wrath of Khan