Researchers finally find the head of mysterious worm fossil

CAMBRIDGE, England, June 24 (UPI) -- Over the last three decades, scientists have modeled the Hallucigenia worm in all the wrong ways. Its befuddling fossil had researchers recreating its likeness upside down, back-to-front, sideways and worse.

But finally, researchers have located the creature's head using advanced imaging technology.

Hallucigenia is one of the first animals to show up in the proliferation of fossils known as the Cambrian explosion. It's a worm-like marine animal outfitted with legs and spikes, and a head that looks a whole lot like its tail.

In the form of a 500 million-year-old fossil, the worm's anatomical symmetry has resulted in a succession of confused scientists. But researchers at the University of Cambridge were able to get an in-depth look at the fossil using electron microscopy.

"Early studies did not realise that parts of the body were buried, and parts of the fossil were not actually part of the animal -- leading to the somewhat wacky early interpretations," researcher Martin Smith told NewScientist.

But exploring beneath the fossil surface, researchers were able to find the creature's buried head with two tiny eyes and a mouth ringed with teeth. What scientists had thought was the animal's head was actually just a squished guts, which likely oozed out as the creature was trapped in a mudslide.

Smith has been studying Hallucigenia for several years. Last year, he and his colleagues produced research definitely linking the creature to modern legged worms like velvet worms -- ending decades of classification confusion.

"An exciting outcome of this study is that it turns our current understanding of the evolutionary tree of arthropods -- the group including spiders, insects and crustaceans -- upside down," said Javier Ortega-Hernandez, co-author of the 2014 study.

The latest research is published in journal Nature.