Cnidocyte of the blubber jelly, Catostylus mosaicus as seen under a scanning electron microscope. Credit, Meredith Peach.

Many people have experienced the painful sting of a sea jelly but did you know that the stings are caused by thousands of microscopic stinging cells called “cnidocytes”? When a potential predator or prey encounters the sea jelly’s tentacles, thousands of stinging cells simultaneously eject a microscopic harpoon-like structure that can penetrate the skin and inject a toxin. The potency of the toxins varies among species. Most sea jelly stings only cause mild irritations to humans but some jellies, such as the box jelly (Chironex fleckeri), can be deadly. Fortunately an anti-venom is now available to treat people stung by box jellies.

Thousands of cnidocytes being disharged from the highly venomous box jellyfish, Chironex fleckeri. Credit Jamie Seymour, James Cook University.
Cnidocyte of the blubber jelly, Catostylus mosaicus as seen under a scanning electron microscope. Credit, Meredith Peach.

Many people have experienced the painful sting of a sea jelly but did you know that the stings are caused by thousands of microscopic stinging cells called “cnidocytes”? When a potential predator or prey encounters the sea jelly’s tentacles, thousands of stinging cells simultaneously eject a microscopic harpoon-like structure that can penetrate the skin and inject a toxin. The potency of the toxins varies among species. Most sea jelly stings only cause mild irritations to humans but some jellies, such as the box jelly (Chironex fleckeri), can be deadly. Fortunately an anti-venom is now available to treat people stung by box jellies.

Unlike cnidarian jellies, comb jellies do not contain toxins and do not sting. Instead, comb jellies use sticky cells (colloblasts) to collect their prey. Whereas sea jelly stinging cells are harpoon-like and deliver toxins, the sticky cells of the comb jellies act like glue and adhere to zooplankton. Since comb jellies don’t have toxins they are completely harmless to humans.