Sea Slug Antenna Jammers
Usually when sea creatures secrete an ink cloud, it acts as a distraction that allows for a quick exit from an impending predator. Inherently, sea slugs could never make that fast an exit – so the ink was always a mystery. Recently though some boffins worked out that the ink actually acts as a jammer of sorts; covering the predators antenna and causing sensory interference within the predator.
Also, the Sea Hare looks well-jazzy in the process. (source)