Other Regenerative Organisms
For metazoans, the ability to regenerate complex structures is widespread. These invertebrates, unlike urodeles, can achieve bi-directional regeneration. Each cut fragment responds by regenerating into a new organism, unlike urodeles that display unidirectional regeneration (1).
|One of the most well known regenerative organisms is the worm. Planaria, a member of the nematode or flatworm phyla, can regenerate individual organisms after being cut into hundreds of pieces. Annelids and Platyhelminthes (segmented and round worms respectively) also have extensive regenerative capabilities. Instead of creating the blastema through dedifferentiation, they turn to neoblast cells. These cells remain in an unspecialized stem cell state and can develop when necessary (15).|
A group of organisms that displays unidirectional limb regeneration (the type exhibited by salamanders) are arthropods (crustaceans and insects). They regenerate their limbs through molting. Throughout their lifetime, arthropods shed their exoskeleton to revel completely new structures. Any damage to the limbs or exoskeleton that does not result in death is replaced after the next molt. Autonomy or amputation of the limbs can even trigger a molt to happen sooner (14).
In mammals, regeneration has been observed. The tip of the finger, especially in children, can be regenerated if the wound is left open and not surgically covered with skin. Mice have similar capabilities with the tips of their toes and tail. However, this kind of regeneration is based on stem cells and is much less complex than limb regeneration (14). Many larval animals also have the ability to regenerate. Ultimately though, it is only urodele amphibians that have the ability to regenerate full limbs at any stage in their life.
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