Video: How a bizarre ancient worm used to walk

It’s easier to be bamboozled by a worm than you might think. This enigmatic 508-million-year-old worm-like creature has been tricking scientists since the 1970s. Reconstructions of what it would have looked like had it upside down, on its side and even back to front.

Now Martin Smith of the University of Cambridge and his colleagues think they finally have the correct description of this creature, which lived during the Cambrian explosion when most major animal groups first emerge in the fossil record.

Hallucigenia was a worm-like marine animal with legs, spikes and a head that is difficult to distinguish from its tail. It is only a few centimetres long, and its body is as thin as a pin.


The late evolutionary biologist Stephen Jay Gould once recounted how Simon Conway Morris, the palaeontologist who coined the name Hallucigenia, chose it because the creature reminded him of something he’d once seen on a trip – “and I don’t mean to Boston”.

Wacky interpretations

“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,” says Smith.

Now, his team has used electron microscopy to describe the creature in unprecedented detail.

As thin as a pin and as prickly as one too (Image: Martin R. Smith)

What was once thought to be its head is in fact just a dark stain that could have been gut contents that oozed out as the animal was flattened in a submarine landslide. So they dug away the sediment around the other side of the animal to reveal its head.

There, they found a pair of simple eyes, which sat above a mouth with a ring of teeth. Its throat was also lined with needle-shaped teeth, which are thought to have worked like a ratchet, keeping food from slipping out each time it took another “suck” at its food.

The findings could help us understand the evolution of moulting animals, a diverse group that includes arthropods, velvet worms and water bears. The teeth resemble those from many other early moulting animals, suggesting that a tooth-lined throat was present in a common ancestor, the team says.

Smith thinks that we now have the final and correct view of what Hallucigenia really looked like. “But with a creature so bizarre and full of surprises, you never know what else it might have up its sleeve.”

Journal reference: Nature, DOI: 10.1038/nature14573