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Starfish don’t have brains. They digest their food externally. And they can regenerate parts of their bodies.

In other words, they are freaks of nature, Science Alert reported.

These creatures belong to a group of marine life known as echinoderms, which include sea urchins and the sea cucumber. These species are unique because their body symmetry is mostly fivefold, rather than the bilateral ‘left-right’ symmetry that exists in most creatures.

“In their bilateral relatives, the body is divided into a head, trunk, and tail,” explained study co-author Jeff Thompson. “But just looking at a starfish, it’s impossible to see how these sections relate to the bodies of bilateral animals.”

This strange symmetry has puzzled scientists for years. As a result, Thompson and his team sought to understand how echinoderms evolved and where they fit in the deuterostome superphylum – a large group of animals that includes both vertebrates and echinoderms.

In their paper, they localized the precise DNA and RNA sequences in a tissue sample taken from a species of starfish known as bat stars. They then created a three-dimensional map of gene expression in the body of the starfish as it grew.

Researchers investigated transcription factors involved in the front-to-back development in bilateral animals. They found genes for developing arms. However, those responsible for trunk development in other deuterostomes were missing.

The findings suggested that sea stars and other echinoderms don’t have a body. They are literally just heads crawling around the sea floor, according to researchers.

The study sheds some new details about the long evolution of echinoderms, with the authors theorizing that at some point they had a body – but dropped it somewhere along the way.

It worked out fine in the end.

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