Biology Question #498

Christina, a 16 year old female from Orland Park asks on January 2, 2002,

What process does a jellyfish go through when it stings something?

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The answer

Peter Fankboner answered on January 3, 2002

Jellyfish, anemones, corals, and hydroids all belong to the Phylum Cnidaria, and a principal characteristic of this group is the presence of stinging cells called cnidocytes. Within each cnidocyte is a capsule (the cnidocyst) which contains a hollow thread and a fluid which is neurotoxic. When this capsule is discharged, strings of proteins in the capsule fluid break up into many fragments, and this produces a rapid rise in the osmotic pressure capsule which forces the hollow thread (which is fastened to the capsule wall) to be turned inside out (like the finger of a rubber glove) as it is fired towards the food item the jellyfish is trying to capture, or an enemy which is threatening the jellyfish. The hollow stinging thread is sent towards the food or enemy at a very high rate of speed and is able to penetrate most living materials, much like the piece of straw that is blown into a tree during a tornado. The hollow thread now acts as a conduit for the capsule's toxin, and the latter either kills its target outright or puts it to sleep. Here is an animation showing how the stinging cells work.

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