One of the creatures found in the Burgess Shale that defies classification by our traditional scheme. It was originally reconstructed as an arthropod, to fit the scientific prejudice that all primitive fossils should fit into recognizable modern groups.

When modern dissection techniques were applied to Opabinia, it was found that the creature lacked any of the jointed appendages common to all arthropods. Proper reconstruction also showed that it had gills attached to the dorsal surface of the lobes of its body (arthropods have gill branches attached to their legs).

The animal has a single appendage, shaped like a clawed nozzle, at the front of its body. This limb was originally interpreted as a fused pair of antennae, possibly used in mating or combat. However, no antenna structure was ever found, and since the nozzle is exactly the right length to reach Opabinia's mouth on the bottom of its head, the nozzle is now thought to be a feeding appendage built something like a vacuum cleaner's hose.

Opabinia is a creature that resembles an arthropod in many ways - even with its five stalked eyes and its vacuum cleaner nozzle, it's hardly the weirdest creature found in the Burgess Shale - but it simply doesn't fit into any recognizable phylum.