Some animals are so good at regeneration that detached piece of one individual can grow into an entirely new organism all on its own. Some species of sea star (known commonly but erroneously as "starfish") use asexual reproduction via fragmentation as their main reproductive mode.

The nematode S. mediterranea can even re-grow its head and brain when decapitated. And the decapitated head can re-grow a completely new body. A slice down to about one cubic millimeter can create a whole new (while tiny) individual with the exact same genome, which can grow from a tiny fragment into a normal sized nematode.

The sea star's ability to regenerate is a little less impressive. It can only regenerate from an arm if the arm takes part of the animal's "central disk" with it. In some species the arm actually pulls away from the body and detaches itself, then heads off to form a new, genetically identical, organism.