2023-11-07 09:00:00
The starfish does not have a body, but only an enormous head whose extensions have been mistakenly called arms. They are composed of cells that are, genetically speaking, almost entirely the head.
If you were asked the question, you probably wouldn’t hesitate. How many arms does a starfish have? Common mortals would respond in chorus 5. Well, this answer turns out to be inaccurate, explains us Naturerelaying a study carried out by American scientists.
In fact, the starfish slowly evolved to take its current form. These animals are mainly found in the oceans. There are around 1,500 species, grouped into thirty families, proving the tremendous diversity of this marine animal, also called asterias. With a life expectancy of almost five years, the starfish feeds mainly on small fish.
Than a head
When we look at a starfish, we often have the impression that it has arms. In reality it would just be… just a huge head. A molecular analysis allowed scientists to trace the evolutionary history of the species. The ancestors of today’s asterias thus did not have “branches” on the sides.
This puzzling creature is not a fish, contrary to what its English name (“star fish”) suggests. But just as it does not have fins, the starfish does not have arms. “We call them starfish arms because we are accustomed to thinking of things that come out of the body as arms and legs” explains Daniel Rokhsar, professor at the University of California at Berkeley, in comments echoed by the Washington Post.
Original symmetry
Very often, for most animals (dog, cat, mouse, whale, etc.) it is simple to find the end of the two bodies, namely the head and the tail. But species such as starfish and also sea urchins have quintuple symmetry, that is to say that their bodies can be divided into five sections.
According to Thurston Lacalli of the University of Victoria in Canada, the starfish is actually a “disembodied head walking on the seabed with its lips”. Now it is up to paleontologists to survey the seabed in order to understand how this animal could have mutated in this way. The starfish has not yet finished revealing its secrets.
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