Have you ever been stung by a jellyfish? Have you ever touched a moon jelly and wondered why you weren’t stung? Do you wonder why turtles can eat jellyfish (with their MOUTHS?)
Jellyfish have tentacles that drift underneath from their bell that are covered in thousands and thousands of cnidoblasts. Cnidoblasts have nematocysts with a coiled thread in them, that are triggered by a tiny follicle on the outside.
Once an object comes into contact with the tentacle, the follicle triggers the nematocyst to uncoil a thread and send out a stinging venom. Imagine a garden hose coiled suddenly filling with water and straightening out…that’s what a jellyfish sting is, except times a thousand!
Members of cnidaria have nematocysts (also corals and anemones), but they have varying degrees of toxicity. The stronger the venom, the worse the sting feels. Something like a moon jelly has a very mild sting, so most people don’t notice any reaction when touching a one in a touch tank, or at most a very mild reaction. Whereas the box jellyfish is so poisonous, its sting can kill humans in minutes.
Sea turtles and other animals eat live jellyfish drifting in the sea. They are also stung as they eat them as well, but like humans with moon jellies, have tough skin and don’t notice or aren’t bothered by the reaction.
These poisonous stings work for self defense and for self preservation: all food that drifts into contact with the tentacles gets stunned and then brought up to the jellyfish stomach for digestion (in the bell!)
Jellyfish are 95% water. But they are amazingly interesting! Have you ever experienced the amazing unfurling of jellyfish nematocysts? Ouch!
Learn more about sea jellies this summer at the Aquarium of the Pacific, Summer of Jellies!