Turns out starfish don’t have arms – they’re “just a head crawling along the sea floor”


Starfish are known for their adorable and symmetrical arms that seem to embrace everything they touch. But it turns out they might not be hugs after all — because starfish, researchers found, are basically “just a head.”

Having radially symmetrical arms is an iconic feature of starfish, but in new research published in the journal Nature Last week, researchers from England’s University of Southampton said the creatures significantly lack the genetic codes for animal torsos and tails. They also found that the genetic codes generally associated with heads were found in the center of starfish arms, meaning the seemingly headless creatures are actually anything but.

“It’s as if the sea star lacks a trunk altogether and is best described as just a head crawling along the sea floor,” said the study’s lead author Laurent Formery in a news release. “This is not at all what scientists have assumed about these animals.”

The University of Victoria’s Thurston Lacalli offered a similar comparison to the team’s results.

“You could think of a starfish’s body … as a disembodied head walking around on the ocean floor on its lips — the lips have sprouted a fringe of tube feet, which was chosen from their original function of sorting food particles, the walk,” Lacalli said . “… This is indeed a radical transformation of the ancestral bilateral body plan.”

Starfish are echinoderms, a type of marine invertebrate known for radial symmetry and spiny skin. Scientists said most animal species have similar genetic structures, prompting them to investigate how echinoderms’ unique makeup came to be in “one of the most enduring zoological puzzles.”

“If you peel away the skin of an animal and look at the genes involved in defining a head from a tail, the same genes code for these body regions across all groups of animals,” study author Christopher Lowe said in ScienceDaily. “So we ignored the anatomy and asked: Is there a molecular axis hidden beneath all this strange anatomy, and what is its role in a starfish forming a pentagonal body plan?”

To find out, they used a new form of genetic sequencing called HiFi sequencing, which according to a news release“can extract very accurate data from gene-sized intact DNA strands, making the process much faster and cheaper.”

Study co-author David Rank said this process allows them to do months of work “in a matter of hours.”

“These advances meant that we could essentially start from scratch in an organism that is not typically studied in the laboratory and put together the kind of detailed studies that would have been impossible 10 years ago,” he said.

What they found is that starfish do not have a head-to-tail axis that runs from the middle to the arms, from the top to the abdomen, or from one side of the arms to the other. Instead, the press release states, “they saw that gene expression similar to the forebrain of humans and other bilaterally symmetrical animals was located along the midline of the sea stars’ arms, with genetic expression similar to the human midbrain toward the arms’ outer edges.”

The only place in starfish where scientists found genes corresponding to animal strains was at the edges of the starfish’s arms.

“These findings suggest that echinoderms, and sea stars in particular, have the most dramatic example of uncoupling of the anterior and trunk regions that we are aware of today,” Formery said. “It just opens up a whole host of new questions that we can now start to explore.”


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