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The diagram shows the anatomy of a nematocyst cell and its ‘firing’ sequence - from left to right. On the far left is a nematocyst inside its cellular capsule. The cell’s thread is coiled under pressure. When potential prey makes contact with the tentacles of a polyp, the nematocyst cell is stimulated. This causes a flap of tissue covering the nematocyst to fly open. The middle image shows the open tissue flap, the rapidly uncoiling thread with barbs along thread. On the far right is the fully extended cell. The barbs of the nematocyst are designed to stick into the prey and inject a poisonous liquid. When subdued, the polyp’s tentacles move the prey toward its mouth and the nematocysts recoil back into their capsules. Figure credit: NOAA
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