Scientists have discovered that they had completely misunderstood this marine creature.
Sea stars are, by any definition, among the world’s weirdest animals. They have no blood and no brains. They eat by vomiting their stomach out of their mouth and engulfing prey within it. They move around on thousands of tiny tube feet. And many have the extraordinary ability to regenerate lost body parts - some can even form an entirely new sea star from a single “arm” and part of the central disk.
The anatomy of these bizarre echinoderms has puzzled researchers for years. With no discernible head, scientists had thought that sea stars don’t have one. Now - according to research published in the journal Nature - the opposite is true. Sea stars are actually all head and no tail.
“It’s as if the sea star is completely missing a trunk and is best described as just a head crawling along the seafloor,” lead researcher Laurent Formery, a biologist from Stanford University and the University of California, Berkeley, says in a statement from Chan Zuckerberg Biohub, which funded the study. “It’s not at all what scientists have assumed about these animals.”
Sea stars, also known as starfish, are part of a group of animals called echinoderms, which includes sea urchins and sand dollars. These creatures are often characterized by a classic five-fold symmetry - meaning you could split them up into five identical sections. Humans and most other animals, on the other hand, have bilateral symmetry - meaning we can be separated down the middle into two equal parts.
Be that as it may, researchers say that the ancestors of sea stars did have trunks and that this indicates that somewhere along their evolutionary journey, sea stars lost these genes -though when that happened is still a mystery. Next, the research team plans to look back in the fossil record to pinpoint exactly when sea stars lost their torsos, reports Scientific American. They also plan to see whether the “all head” pattern holds up for sea urchins and sea cucumbers, too.