Wiwaxia

One of the many incredibly unique creatures discovered 

• Wiwaxia fossil
• This particular preparation also contains a fossil of Marrella at the upper left. 

during the excavation of the Burgess Shale is  Wiwaxia, 

a creature which even today has not been classified into 

any existing animal group.   Wiwaxia is distinguished by a double row of elongated spines which rise upwards from it's back. The rest of its body was covered in overlapping, scale-like segments called sclerites which were arranged in different orientations depending on their position on Wiwaxia's body.. Evidence suggests that Wiwaxia grew by molting these plates. The sclerites along with the rows of spines probably offered protection for Wiwaxia, a small creature ranging from 3 to 55 mm in length, from predators. Another defining feature of Wiwaxia was it's anterior jaw, which had two rows of teeth; it's position suggests the bottom feeding nature of the creature.

The classification of Wiwaxia has always been a challenge for scientists. 

There were no sclerites on the bottom of the creature and its soft body moved across the sea floor using bands of muscle in a way that is reminiscent of a slug. This brings to mind images of the mollusk family, but Wiwaxia's sclerite armor is not a characteristic of mollusks. Charles Walcott, the original discoverer of the Burgess Shale and it's fossils, placed Wiwaxia with the annelids, calling it a polychaete annelid or bristle worm. Conway Morris, who helped to disprove many of Walcott's original classifications, argued that Wiwaxia's sclerites weren't like those of other polychaete.

As a result of all the unique features of Wiwaxia and the debate between scientists, Wiwaxia has yet to find a home in any known animal group. Instead it joins the ranks of ranks of other Burgess Shale "oddballs" like Hallucigenia and Anomalocaris.