What are Planarians?
A planarian is a (mostly) free-living flatworm of the class Turbellaria, under the phylum Platyhelminthes. Moreover, the term “planaria” is actually the name designated to one genus, however, the name “planarian” can be used to describe any member of the family Planariidae. Planarian flatworms also have “eyes” (ocelli) that look cross, giving them an almost cartoonish appearance.
Planarians are very interesting animals because of the fact that they can regenerate lost body parts which would be fatal for any other animal. For instance, if you can split a planarian down the middle, the two halves can regenerate into two separate individuals. If you cut a planarian into many pieces, each piece will regenerate a new flatworm.
Key to Regeneration
Schmidtea mediterranea, a planarian, has specialized stem cells called neoblasts. The neoblasts are crucial for the process of regeneration, where missing tissues are regenerated after an injury. Furthermore, neoblasts are the only dividing cells of the adult animal. This is comparable to pluripotent stem cells in humans – however, these cells do not remain after birth. Hence, neoblasts in planarians are the key to regeneration since these are the only type of cells that survive into adulthood and are capable of division in the adult animal.