We share the Earth with millions of creatures, from gigantic marine animals to insects and smaller beings. Each of them has its intrinsic characteristics that differentiate them from the others and have developed their own evolutionary path to ensure their permanence in the jungle of life.
But in most cases, their survival is also limited to avoid overpopulation and maintain balance in the food chains. Thus, we face the hazards of life and other factors such as reproduction, in order to continue to subsist. However, the planaria worm is the exception.
What is the planaria worm?
Planaria is part of the family Planariidae, represented by only one species, Planaria torva or simply planaria. We could say that it is a small freshwater worm that defies everything we know about biology and adaptation; in other words, a true jewel of evolution.
The secrets hidden in its small organism are such that it has been considered immortal. Although its body is not very intricately engineered, it is at the same time one of the most complex organisms scientists have ever encountered. This small worm has the great capacity to regenerate itself and has even developed the ability to regenerate all parts of its body, including organs.
Other animals such as the salamander also share this ability, however, if their heads are cut off, the animal will die. Contrary to what happens with the planarian, if you cut it in several sections, then you will get not one, but as many planarians as you have cut the animal. Each of its dissected pieces will generate complete new planaria, including the head, organs, tissues, and everything necessary to ensure its survival.
But its morphology is also very different from what we commonly know. Its face differs from other animals because of two very remarkable characteristics. First, where its eyes should be placed, it has only two spots that it uses as photoreceptors to see. Secondly, the planarian’s mouth does not appear on the face but is located much lower, very close to the stomach. In fact, its mouth is closer to its tail than to its head.
How do planaria reproduce?
In terms of reproduction, planaria also defy evolutionary theories. All planarians are hermaphrodites, meaning that they possess both female and male sex organs. But in an even more surprising fact, scientists have discovered that planaria are capable of reproducing through both sexual and asexual reproduction.
In sexual reproduction, all planarians can both give and receive sperm due to their hermaphrodite characteristic. However, and contrary to all other animals, the eggs remain inside until days before hatching, when they are expelled as capsules. And although this is surprising enough, their asexual reproduction is even more so.
Planarians dissect themselves, separating the tail from the rest of their body. After this happens, the detached part works its magic and regenerates the remaining body, while the original planarian gets its tail back. In other words, when there are no individuals to reproduce, the planarian splits in two in order to survive.
Its magnificent evolution
The peculiar characteristics of the planaria have made experts turn their attention to this fantastic animal. Many believe that it hides within its small organism the secret of immortal life, which could be due to the fact that 25% of its cellular tissue is made up of stem cells.
However, it is not yet fully understood why this freshwater worm has developed such characteristics. Much less is fully understood how such regenerative capacity works. In the meantime, researchers are trying to decipher this evolutionary gem that defies everything we know about animals.
Story originally published in Ecoosfera