What it was
A spiny, legged worm about the length of your little finger, from the Burgess Shale in the Canadian Rockies, 508 million years old. It walked on paired legs with fourteen spines standing along its back as armor.
How we got it wrong
In 1977 it was drawn walking on its spines, with tentacles on its back. In 1991 a second row of legs turned up hidden in the rock, and the drawing was flipped. In 2015 its real head, with eyes and a toothed mouth, was found at the other end.