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  • You're swimming in the ocean when something brushes your leg.

  • When the tingling sets in,

  • you realize you've been stung by a jellyfish.

  • How do these beautiful, gelatinous creatures pack such a painful punch?

  • Jellyfish are soft because they are 95% water

  • and are mostly made of a translucent gel-like substance called mesoglea.

  • With such delicate bodies,

  • they rely on thousands of venom-containing stinging cells called cnidocytes

  • for protection and prey capture.

  • Even baby jellyfish, the size of a pencil eraser,

  • have the ability to sting.

  • Larval jellyfish, ephyrae, look like tiny flowers pulsating in the sea.

  • As they grow, they become umbrella-shaped with a bell at the top

  • and descending tentacles around the margin.

  • The largest species of jellyfish, the lion's mane,

  • has tentacles that can extend more than 100 feet,

  • longer than a blue whale.

  • These tentacles contain most of the stinging cells,

  • although some species have them on their bells, too.

  • Venom is ejected via a nematocyst,

  • a whip-like hollow tubule,

  • which lies coiled under high osmotic pressure.

  • When mechanical or chemical stimuli activate an external mechanical

  • the lid of the cell pops open and sea water rushes in.

  • This forces a microscopic barbed harpoon to shoot out,

  • penetrate and inject venom into its victim.

  • Nematocyst discharge can occur in less than a millionth of a second,

  • making it one of nature's fastest biomechanical processes.

  • Nematocysts can continue to fire even after a jellyfish has died,

  • so it's important to remove lingering tentacles stuck to the skin.

  • Rinsing with vinegar will usually render undischarged nematocysts inactive.

  • Seawater can also help remove residual nematocysts.

  • But don't use fresh water because any change in salt balance

  • alters the osmotic pressure outside of the cnidocyte

  • and will trigger the nematocyst to fire.

  • That's why urinating on the affected area, a common folk remedy,

  • may do more harm than good, depending on the composition of the urine.

  • Most jellyfish stings are a painful nuisance,

  • but some can be deadly.

  • An Indo-Pacific box jelly, also called a sea wasp,

  • releases venom which can cause contraction of the heart muscles

  • and rapid death in large doses.

  • There's an anti-venom, but the venom is fast-acting,

  • so you'd need immediate medical intervention.

  • Despite the impressive power in their tentacles,

  • jellies aren't invincible.

  • Their stinging cells are no match for the armor of thick-skin predators,

  • like the leatherback turtle and ocean sunfish.

  • These predators both have adaptations that

  • prevents slippery jellyfish from escaping after they are engulfed:

  • backwards pointing spines in the turtle's mouth and esophagus

  • and recurved teeth behind the sunfish's cheeks.

  • Even tiny lobster slipper larvae can cling to the bell of a jellyfish

  • and hitch a ride,

  • snacking on the jelly while they preserve their own energy for growth.

  • Small agile fish use the jellies as moving reefs for protection,

  • darting between tentacles without ever touching them.

  • Nudibranchs, which are sea slugs covered in protective slime,

  • can actually steal the jelly's defenses by eating the cnidocytes

  • and transferring them to specialized sacks for later use,

  • as weapons against their own predators.

  • Even humans might benefit from the sting of a jellyfish one day.

  • Scientists are working on manipulating cnidocytes to deliver medicine,

  • with nematocysts rarely 3% of the size of a typical syringe needle.

  • So, the next time you're out in the ocean, be careful.

  • But also, take a second to marvel at its wonders.

You're swimming in the ocean when something brushes your leg.


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B2 中上級

TED-ED】クラゲはどうやって刺さるのか?- ネオシャ・S・カシェフ (【TED-Ed】How does a jellyfish sting? - Neosha S Kashef)

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    SylviaQQ に公開 2021 年 01 月 14 日