Animals that regenerate

Species that regrow limbs, organs or whole bodies from fragments.

• AxolotlAmbystoma mexicanum
• Hydra vulgaris
• Immortal JellyfishTurritopsis dohrnii
• Starlet Sea AnemoneNematostella vectensis
• Purple StarfishAsterias rubens
• Golden Star TunicateBotryllus schlosseri
• Holothuria forskali
• Common EarthwormLumbricus terrestris

About this list

Regeneration is patchily distributed and probably ancestral, with most animal lineages having lost much of it rather than a few having invented it. Hydra has no evident limit: cut into pieces, each fragment reassembles a whole animal, and the same cells that make this possible appear to prevent it ageing in the ordinary sense.

Turritopsis dohrnii goes further still. Faced with starvation or injury, the adult medusa reverts to the polyp stage and starts its life cycle again, which is the basis of its popular billing as the "immortal jellyfish" — accurate as far as senescence goes, though the animals are eaten and infected like anything else.

The axolotl is the workhorse of the field because it regenerates a complete limb, correctly proportioned and oriented, over and over, without scarring — and because it is a vertebrate, so what it does is at least in principle relevant to us.