After all, the “arms” of sea stars are the heads

The puzzle is an old one: Experts have long tried to understand how creatures like sea stars, sea urchins and other animals with a pentagonal body plan, known as echinoderms, evolved from an ancestor with double symmetry, a body plan common in animals, including insects, molluscs and vertebrates. .

“How the different body parts of echinoderms relate to those we see in other groups of animals has been a mystery to scientists throughout their study,” said Geoff Thompson, co-author of the study from the University of Southampton. “In their dioecious relatives, the body is divided into a head, torso, and tail. But looking at starfish, it is impossible to see how these divisions relate to the bodies of dioecious animals.”

In the new study, led by Laurent Formieri and Chris Lowe of Stanford University, scientists used a variety of high-tech molecular and genomic techniques to understand where different genes are expressed during sea star development and growth. The researchers created a 3D map of genetics in starfish and discovered where specific genes are expressed during development – genes that control the development of the ectoderm, which includes the nervous system and skin.