Spirocysts (Sticky Thread Cells)

A capsule with a coiled thread

Sea anemones and corals are ocean animals. A sea anemone sits on a rock and waves its soft tentacles in the water. Corals are its close cousins.

Their tentacles are covered with spirocysts. Each one is a tiny capsule with a long thread rolled up tight inside, like a spring in a box.

Jellyfish and anemones also have stinging cells that inject venom. Spirocysts are different. Their threads don't sting. They are sticky.

Sticky tape for grabbing

When something touches the tentacle, the spirocyst fires. The thread shoots out and unrolls.

The thread is covered in super tiny hairs that spread out into a sticky tangle, like a spider web. The tangle sticks to small animals that swim by, so the anemone can hold on to its food.

Scientists think spirocysts also help anemones stick to rocks and other things around them.

Spirocyst quiz