From Creatures Wikia
The Pest Jellyfish is an underwater inhabitant of Aquatilis Caverna that is related to the regular jellyfish. However, unlike their counterparts, these nasty critters can give your Creatures quite a shock! They seem to be a vegetarian, but if agitated enough, they morph into a much larger stage with a heart-shaped bell. If placed onland, their tentacles are retracted, they become unconscious, and if the jelly is large, it will shrink back down. Placing it back in water will revive them.
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