A weird creature that lived half a billion years ago and is distantly related to modern insects and crustaceans has bared its teeth to scientists.
For the first time, experts have been able to identify features of Hallucigenia's head, including its simple eyes and needle-like teeth.
The unearthly animal looks as if it belongs in a sci-fi movie. Measuring up to five centimetres long, Hallucigenia had a worm-like body, seven pairs of legs ending in claws, and a back sprouting long spines.
Its discovery in the 1970s had scientists completely confused as they reconstructed the creature backwards and upside down.
Hallucigenia's pairs of spines were thought to be its legs, its legs were thought to be tentacles along its back, and its head was mistaken for its tail.
But until now, no one had been able to give the strange beast a face.
The new study involved a microscopic examination of Hallucigenia fossils from the Royal Ontario Museum, Canada, and Smithsonian Institution in the US.
Dr Jean-Bernard Caron, from the Royal Ontario Museum, explained how the team removed sediment covering one end of the creatures, which died in mud 508 million years ago.
He said: "This let us get the new images of the head. When we put the fossils in the electron microscope we were initially hoping that we might find eyes, and were astonished when we also found the teeth smiling back at us."
The images show an elongated head with a pair of simple eyes sitting above a mouth encasing a ring of teeth, which also lined the animal's throat.
The teeth probably flexed in and out to generate suction, helping Hallucigenia to draw in food, said the scientists writing in the journal Nature.
Lead author Dr Martin Smith, from Cambridge University, said: "Prior to our study there was still some uncertainty as to which end of the animal represented the head, and which the tail.
"A large balloon-like orb at one end of the specimen was originally thought to be the head, but we can now demonstrate that this actually wasn't part of the body at all, but a dark stain representing decay fluids or gut contents that oozed out as the animal was flattened during burial."