We already knew that starfish were pretty weird. These strange sea creatures seem to have their own rules. They are brainless and bloodless, digest food they take in from outside, and regenerate their body parts, sometimes turning into completely new starfish. But none of them are the worst. Starfish and other echinoderms lack the architecture necessary for a real body, according to a new analysis of their gene expression.

A team led by biologists Laurent Formery and Chris Lowe of Stanford University says these are actually just moving heads that reveal the ability to crawl.

“In terms of ectoderm patterning,” the researchers write in their paper, “Echinoderms are predominantly head-like animals.”

Echinoderms are not only starfish, but also sea urchins, sand dollars, sea cucumbers; They are so common in parts of the ocean that humans frequently visit that we tend to think of them as something unusual. If we consider them too. But they are very different from other animals. Body symmetry is (usually) fivefold, not the bilateral left-right symmetry we see in most creatures.

The oldest known starfish in the fossil record predates the oldest known dinosaurs by 200 million years, so whatever they do, they do it very, very well. But their strange symmetry means their bodies are difficult to understand.

“How the different body parts of echinoderms relate to parts we see in other animal groups has been a mystery to scientists for as long as we’ve been studying them,” says Geoff Thompson, an evolutionary biologist at the University of Southampton in the United Kingdom.

“In their binary relatives, the body is divided into head, trunk and tail. However, it is not possible to understand how these parts are related to the bodies of bipedal animals just by looking at the starfish.”

Researchers conducted a molecular study to find out where echinoderms fit into the superphylum bivalves, a large group of animals that includes both vertebrates and echinoderms. Because bivalves evolved from a common ancestor millions of years ago, researchers thought they could trace the evolutionary path of echinoderms.

Their research was done on starfish called starfish. Patriria miniataor bat stars.

They used RNA tomography and a technique called in situ hybridization, in which scientists localize precise sequences of DNA and RNA in a tissue sample. They used this information to create a three-dimensional map of gene expression in the starfish’s body as it grew.

They examined a set of transcription factors found in bilateral animals that are involved in the back-and-forth development of the creature’s body, a process known as anteroposterior patterning. These genes were found in starfish; They help develop the arms from approximately the middle to the tip. But there was a glaring omission. Other dicotyledons have a set of genes that help develop the trunk of the body.