With jellies, envenomation is mainly a contact sport. Lacking bones and muscles (not to mention a nervous system to operate them), these soft, squishy protoplasmic blobs have limited ability to reach out and grab their prey. What they do have are dangling tentacles and oral arms—sometimes quite long—that are loaded with stinging cells. These appendages drift beyond a jelly’s bell in the ocean current—the same moving water that brings planktonic animals, fish larvae and smaller jellies floating by. When an animal bumps into a jelly’s tentacles and oral arms (and in some species, even the bell), the stinging cells fire dartlike nematocysts, loaded with powerful venom, that lodge in the prey’s tissue and slow or immobilize it. Human swimmers who brush against nearly invisible jellies get stung the same way.
Stunned prey is easier to eat—and it’s less likely to wiggle around, reducing the chances a delicate jelly will be torn apart during its meal. Fish- and shrimp-eating jellies have long harpoonlike nematocysts that can penetrate scales or shells. Jellies that eat softer, smaller prey, like the northeast Pacific sea nettle shown here, don’t need that kind of weaponry.
As for the difference between venom and poison, a very general way to remember is that you inject venom and ingest poison. So jellies, with their teeny nematocysts, are venomous. A plate of pufferfish, improperly prepared, is poisonous. Toxicity, by any name, is a stunningly effective adaptation. We’ll explore that more next week.
Your ticket to Jazzin’ at the Shedd includes our new special exhibit, Jellies. The species on display will change throughout the summer, so check them out each time you come to Jazzin’.
Posted by Karen Furnweger, web editor