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Worm fossil sheds light on annelid head evolution

An ancient, alien-like worm could help shed light how the creatures evolved over time, a new study in Current Biology reports.

The eyeless species — named Kootenayscolex barbarensis — lived roughly 508 million years ago. It had two tentacles coming out of its head and was covered in a series of hair-sized bristles. Researchers from the University of Toronto discovered the creature in British Columbia. While it had similarities to many modern bristle worm species, it also had some key differences that could help scientists better understand how worms changed over time.

“[U]nlike any living forms, these bristles were also partially covering the head, more specifically surrounding the mouth,” said lead author Karma Nanglu, a doctoral student in the Department of Ecology and Evolutionary Biology at the University of Toronto, according to Live Science.

The team analyzed the fossils, which allowed them to discover how ringed worms — a group that includes modern earthworms and leeches — developed their unique heads. The newly discovered species suggests that the annelid head evolved from posterior body segments that had pair bundles of bristles.

Scientists found 500 individual worm fossils from 2012 to 2016 in Marble Canyon, a site that sits within the Burgess Shale deposit. The specimens are not only interesting from a evolutionary standpoint, but they are also from the Cambrian Explosion, which is when most modern animal groups first appeared in the fossil record.

The worm only measured 1 inch long, but each of its 25 body segments had 56 bristles apiece. It also had two long tentacles on its head that could extend out from its body. Though researchers are not sure, they believe K. barbarensis was a deposit feeder that sifted through the mud to find organic matter.

To get a close look at the species, researchers both studied it under a microscope and through a process known as elemental mapping. They hope further research will shed more light on the species and give them more insight into how worms, as well as other animals, first came about.

“Coupling new fossil discoveries, such as Kootenayscolex, with a deeper understanding of developmental processes presents a powerful tool for investigating these unique morphologies and, ultimately, the origin of modern animal diversity,” said study co-author Jean-Bernard Caron, a researcher at the University of Toronto, in a statement.

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