Closing a wound, regrowing an arm

A cut can close. A missing arm can grow back. Some animals can even let go of part of their own body. Each of these changes has a name.

Three processes to tell apart

1

Wound healing

The wound closes and protects what is inside.
2

Regeneration

A lost part grows back.
3

Autotomy

Some animals can let part of their body break away when threatened.

Where does the new arm come from?

Imagine looking at a sea star that has lost an arm. Its body and other arms are still there. The sea star uses the parts that are still alive to grow a new arm. It takes time.

Picture the missing part. Look first at what stayed alive around the injury.
Two cutaway views of a sea cucumber: without an intestine, then with an intestinal tube forming.
This sea cucumber has lost part of its gut. It can rebuild it. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

A new intestine

A Caribbean sea cucumber can live after losing its intestine. A thin layer of tissue that held the old intestine in place stays inside the body. The new intestine starts to grow there.

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