Scientists Say: Nematocyst | Science News for Students

Scientists Say: Nematocyst

These special cells pack a painful punch
Aug 20, 2018 — 6:30 am EST

This is a sea nettle. Their gently-floating tentacles have nematocysts — special cells with painful barbs inside.


Nematocyst (noun, “knee-MAH-tah-sist”)

This is a special cell found in some ocean critters — such as jellyfish, sea anemones and corals — that has a stinging barb coated in venom. The cell works a bit like a living harpoon. Before the nematocyst fires, its barb stays coiled inside the cell in a chamber where it is bathed in venom. When the nematocyst comes in contact with something else — such as a fish or your leg — the tiny harpoon fires. The barb sinks into the target, delivering a dose of venom.

Nematocysts are most associated with jellyfish. The cells’ venom can range from weak to strong. Australian box jellyfish, for instance, have venom that can kill a person. Corals also have nematocysts. They use them at night to catch tiny creatures floating by in the water.

In a sentence

Jellyfish have nematocysts, but their distant cousins the comb jellies are sting-free.

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Power Words

(more about Power Words)

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

coral     Marine animals that often produce a hard and stony exoskeleton and tend to live on reefs (the exoskeletons of dead ancestor corals).

harpoon     A spear-like weapon that is thrown to pierce an aquatic animal. It’s barbed or hooked head keeps the weapon attached to the animal. An attached rope can then be pulled in, bringing the animal to a hunter’s boat. A harpoon may also be any latching device that pierces a surface to hold onto it.

jellies     (in biology) These are gelatinous animals that drift in water (mostly seawater) or brackish (semi-salty) estuaries. For more than 500 million years, they have moved around the oceans by pumping pulses of water through their jelly-like tissue. Their body often has an umbrella-shaped bell. Trailing from around a central mouth may be many tentacles. Although jellies don’t have brains, they do have a nervous system which can sometimes detect light, movement or certain chemicals. Some members of this family, known as cnidarians, are known as jellyfish. In fact, none are true fish but related to hydras and corals.

nematocyst     Stinging cells in the tentacles of jellyfish, hydra and related animals. The toxins released by these cells help immobilize prey and ward off attackers.

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

venom     A poisonous secretion of an animal, such as a snake, spider or scorpion, usually transmitted by a bite or sting.