An ancient arthropod has puzzled scientists so much, they called him Hallucigenia: it can only come from a hallucination!

In 1979, Simon Conway Morris discovered a new type of animal fossil in the shale of British Columbia, Canada. He'd been uncovering remains of the Burgess Shale Worm when he found this other animal.

After studying it's remains, Morris determined that the animal just did not make any sense and he dubbed it "Hallucigenia" because it fit more in the realm of hallucinations than reality.
After further research, experts now think Hallucigenia is related to modern day arthropods. It is slender and worm-like with a poorly formed blob on one end of it's body.

It had seven pincer-tipped tentacles on one side and seven pairs of jointed spines on the other. Six of the tentacles were paired with spines with the remaining one lined up in front of the spine.

Morris couldn't find a head and couldn't see how either form of Hallucigenia's appendages could be used for locomotion. Some scientists believe that Hallucigenia was just an appendage of a larger creature that existed.