Scientists say that starfish's arms are not limbs, they are just extensions of their heads!

Scientists say that starfish's arms are not limbs, they are just extensions of their heads!

Do you know what really scary Halloween decor can make? A human head crawls into the room on hundreds of tiny feet. In case you're wondering why we're being unnecessarily horrified now that the holiday has already passed, it's because we've been inspired by new findings about starfish.

With multiple “arms” emerging from it, one might think that the starfish had no dearth of limbs. But researchers have found that starfish (or starfish) and other echinoderms like sea urchins, sea cucumbers, and sand dollars are basically just heads!

Confused? Well, most creatures, including humans, have a distinctive head, torso, limbs, and buttocks. And starfish do not. They have an eye on the tip of each arm, and have no distinct body parts, making it impossible for us to guess where their heads begin and their tails end.

While our imaginations led us to believe that the five threads protruding from the creature's main body were its limbs for a time, its genes tell a different story.

Recently, scientists set out to discover why these echinoderms, which have bodies arranged in five equal, symmetrical sections, do not have clear body segments. This was particularly mysterious given that evolutionary records indicate that they evolved from bilaterally symmetrical ancestors, meaning their bodies consisted of two halves that mirrored each other, much like in humans.

To understand the workings of the organism, the researchers built a 3D map of starfish gene expression to determine where specific genes are expressed during development. More specifically, they mapped the expression of genes responsible for the development of the creature's ectoderm, which includes its skin and nervous system.

While they found genetic signatures associated with head growth almost everywhere in the juvenile sea stars they analysed, they were missing something. When the researchers compared the expression of genes tasked with encoding the parts of the torso and tail of starfish with other groups of animals, they found that these important parts of the body plan were missing!

Furthermore, molecular markers typically associated with the front of the animal's head have also been identified near the middle of each of the starfish's five arms.

“It's as if the starfish is missing a torso entirely, and is best described as just a head crawling along the sea floor,” said study co-author and Stanford University evolutionary biologist Laurent Formery.

These new findings have led researchers to speculate that sea stars and other echinoderm ancestors may have evolved their five-segmented body plan by losing the trunk region that their bilateral ancestors possessed. This change must have allowed them to move and feed differently from animals with identical arms.

But if you're wondering why these creatures evolved this way, the oldest known starfish in the fossil record predates even the oldest known dinosaurs by more than 200 million years! So, while they end up looking ridiculous and having creepy heads, they must be doing something right to be able to last this long.

The results of the study were detailed in nature It can be accessed here.


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