Starfish are known for their adorable, symmetrical arms that seem to hug whatever they touch. But it turns out it might not be cuddling after all – because sea stars, researchers have discovered, are basically “just a head.”
Having radially symmetrical arms is an iconic trait of sea stars, but in new research published in the journal Nature last week, scientists at the University of Southampton in England say the creatures significantly lack the genetic codes for torsos and animal tails. They also discovered that genetic codes typically linked to heads were found in the middle of sea stars’ arms, meaning the seemingly headless creatures are actually quite the opposite.
“It is as if the starfish had absolutely no proboscis and was best described as a simple head crawling on the sea floor,” said the study’s lead author, Laurent Formery, in a statement Press. “This is not at all what scientists have assumed about these animals.”
Thurston Lacalli of the University of Victoria offered a comparison similar to the team’s findings.
“One might imagine the body of a starfish… as a disembodied head walking on the seabed on its lips – the lips having grown a fringe of tubular feet, recovered from their original function of sorting food particles, to doing the walk,” Lacalli said. “…This is truly a radical transformation of the ancestral bilateral body plan.”
Sea stars are echinoderms, a form of invertebrate marine animals known for their radial symmetry and spiny skin. The researchers said most animal species have similar genetic structures, prompting them to study how the unique makeup of echinoderms arose in “one of the most enduring zoological enigmas.”
“If you remove 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 in all groups of animals,” said l study author Christopher Lowe in ScienceDaily. “So we ignored the anatomy and asked: Is there a molecular axis hidden beneath all this weird anatomy and what is its role in a starfish forming a pentaradial body plan?”
To figure it out, they used a new form of genetic sequencing called HiFi sequencing, which, according to a press release, “can extract highly precise data from intact, gene-sized strands of DNA, making the process much faster and cheaper.
Study co-author David Rank said this process allows them to complete months of work “in a matter of hours.”
“These advances have allowed us to start from scratch in an organism that is not typically studied in the laboratory and perform the kind of detailed study that would have been impossible 10 years ago,” he said.
What they found is that sea stars don’t have a head-tail axis running from the center to the arms, from the top to the belly, or from one side of its arms to the other. Instead, the press release states, “they saw that gene expression corresponding to the forebrain in humans and other bilaterally symmetric animals was located along the midline of sea star arms, with gene expression matching that of the human midbrain to the arms.” outer edges.”
The only place in sea stars where scientists found genes similar to those in animal trunks was at the edges of sea star arms.
“These results suggest that echinoderms, and sea stars in particular, exhibit the most spectacular example of decoupling of the front and trunk regions that we know today,” Formery said. “This opens up a ton of new questions that we can now start to explore.”