Research shows location of starfish's head

Starfish "essentially is a head without a trunk and limbs that walks with lips," said a new study combining genetic and molecular techniques released by Stanford University on Wednesday.

The study, published in the journal Nature as well, detailed that starfish start life with two-sided body symmetry like humans, but when they grow up, they have a "pentaradial symmetry," which may have upended everything people knew about the anatomy of this animal.

Many scientists have long considered starfish to be headless animals. And this new study showed that the starfish's ancestors lost their trunks and limbs during evolution. This finding helps solve a centuries-old zoological mystery about one of the most puzzling creatures on Earth.

Starfish are a type of echinoderm. Compared to other invertebrates, echinoderms are not too far apart from humans genetically. But the life cycles and anatomy of starfish are very different from most other animals, from whales to mice, which make it easy to distinguish the head and the tail.

A starfish's life begins as a fertilized egg that hatches into free-floating larvae. The larvae then transform from a bilateral (midline symmetrical) body structure into a five-point star-shaped adult, or five-fold symmetry, meaning their bodies can be divided into five equal parts.

The study was funded by the Chan Zuckerberg Biohub in San Francisco as well as NASA, which is interested in how life may evolve on other planets.

The next step of the team, the Washington Post reported, is to study the body plans of sea urchins, sea cucumbers, and other sea star relatives.

"No single species has all the answers," said Zak Swartz, a scientist at the University of Chicago-affiliated Marine Biological Laboratory who studies sea star development but was not involved in the Stanford's study.

"And a big open question remains: What is the origin of fivefold symmetry?" he added. "And why the number five?"