Jellyfish - Pulsating Sea Creature with a Sting

Stinging Cells--What Makes the Cnidarians What They Are!

Like their Cnidarian cousins (the corals, sea anemones, and hydra), jellyfish's main claim to fame are the microscopic stinging cells that coat their tentacles (tendrils or "oral arms") that extend from their main body (their "bell"). These cells, called cnidocytes, contain a specialized organelle called a cnidocyst or nematocyst that holds a barbed venom capsule. When the stinging cell is triggered, the nematocyst fires in a discharge that is one of the fastest biological processes--as fast as 600 nanoseconds an acceleration approaching five-million g. After penetration, the nematocyst injects the neurotoxic venom into the targeted organism (fish and crustaceans--sometimes planktonic), which immediately paralyzes the organism--allowing the jellyfish to either pull it to its oral cavity ("mouth") to eat it or to release it to escape from it.


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Jellyfish do not actively seek out and attack their prey, but rather, float mostly transparently and unseen by their unsuspecting prey that inadvertently ventures into contact with their tentacles and the subsequent firing of the stinging cells.


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A dangerous things about the cnidocytes and nematocytes is that they can fire independently. The animal can be considered "dead", yet the stinging cells can still deliver a nasty sting.




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I experienced this hazard first-hand when I lived on Guam. Occasionally, especially after typhoons, jellyfish and Portuguese Man-o-War would wash up on the beaches around the island. One clear day after such a storm, I was walking along the beach to see what had washed up from the storm. For amusement, I used a stick to turn over rocks to see what was under them and to pop the inflated "sails" of the Portuguese Man-o-War that were laying shriveled and dried along the shore. I did this for about an hour before returning to the road that led to my home. As I walked back home, some mosquitos and other insects tried to get their dinner off my back. I instinctively and reflexively used the stick to scratch my back. Wrong move!--the stick was now entangled with the remains of the tentacles of Portuguese Man-o-War that I had been poking earlier. The moment I touched my back with the stick, an intense pain rose on my back. It was then that I realized what I had done. I dropped the stick and ran home--where my Dad helped with pulling and scraping the stingers and tentacle pieces off my back and making a sauve of baking soda that he smeared on the wounds. I had some nasty and painful sores on my back for quite a while.




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The most deadly cnidocytes (to humans, at least) are those of the box jellyfish (which is not a true jellyfish--but a close relative). One member of this phylum of the Cubozoa class, the sea wasp, Chironex fleckeri, is the one of the most venomous marine animals known. It causes excruciating pain, followed by death, sometimes within two or three minutes. The chance of survival if stung while swimming alone is "virtually zero."

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Another infamous and potentially deadly Cubozoan (box jelly) is the "Irukandji"-a thumbnail-sized jellyfish (Carukia barnesi) that lives mostly off the coast of Australia. The Irukandji is unique among jellyfish in that it not only has stinging cells on its tentacles, but it also has stinging cells on its bell. The venom is injected only from the tip of the stingers rather than from the entire length-resulting in the stingers penetrating deep into tissue before releasing the venom. Quick overall pain and death are the result.

Jellyfish are an important source of food in many Asian countries. Only jellyfish belonging to the order Rhizostomeae (especially Rhopilema esculentum, Mandarin name: haizhe) are harvested for food because they are typically larger, have no tentacles or stinging cells, and have more rigid bodies than other jellyfish.




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Traditional processing methods involve a mixture of table salt and alum, and then desalting, which makes the jellyfish drier and more acidic. Jellyfish prepared this way are about 95% water and 4 to 5% protein, making it a relatively low calorie food.

After trying some when I visited Taiwan and then later when in Japan, I realized that it's sort of an "acquired taste".... to me they taste like dried rubber bands. The addition of soy sauce improves their taste a bit, but not much. However, your mileage may vary--give them a try the next time you visit a Chinese restaurant!

Squid graphic courtesy of Squidoo Squid Graphics For Your Lenses! by GreekGeek.