Wiwaxia is a genus of soft-bodied animals that were covered in carbonaceous scales and spines. Wiwaxia fossils – mainly isolated scales, but sometimes complete, articulated fossils – are known from early Cambrian and middle Cambrian fossil deposits across the globe.[2][3][4] The living animal would have measured up to 5 cm (2 in) when fully grown, although a range of juvenile specimens are known, the smallest being 2 millimetres (0.079 in) long.[4]
Wiwaxia’s affinity has been a matter of debate: researchers were long split between two possibilities. On the one hand, its rows of scales looked superficially similar to certain scale worms (annelids); conversely, its mouthparts and general morphology suggested a relationship to the shell-less molluscs. More recently, evidence for a molluscan affinity has been accumulating, based on new details of Wiwaxia’s mouthparts, scales, and growth history.[4][5]