PART 3 of the Burgess Shale Fossils:

This post is part of a series of six posts dealing with “Middle Cambrian Life: Exceptional Fossils” (Lagerstätt) from the Burgess Shale Member of the Stephen Formation, British Columbia, Canada. Please see my previous two posts; the first of which serves as an introduction to this broad topic.

Wiwaxia corrugata (Matthew, 1899) (new combination) is shown below. There has been considerable controversy about what kind of animal group it represents. It was a soft-bodied, slug-like animal covered in carbonaceous scales and, along its dorsum, with two rows of 7 to 10 blade-like spines. Although some early workers believed that Wiwaxia might be an annelid (worm), that idea has fallen out of favor because Wiwaxia shows no evidence of segmentation. The general consensus is now that Wiwaxia represents a “stem group mollusk” that existed at the time when annelids and mollusks branched off from each other, in an evolutionary sense. Phylum Mollusca (mollusks) is a large group today and consists manily of chitons, scaphopods, bivalves, gastropods, and cephalopods.

The three views below show the bottom (mouth is the "v" shaped structure), top, and side of a plastic replica of Wiwaxia, in that order. The original size of this animal was about 5.5 cm in length.

Some researchers have classified Wiwaxia as a halkieriid, which is a group of Early to Middle Cambrian “small shelly fossils” that consisted of mineralized sclerites, or armored shell plates, which commonly disarticulate upon death. While alive, however, halkieriids looked like slugs in "chain mail."

On its ventral (basal) side, Wiwaxia has a small feeding apparatus consisting of two (rarely three) tooth plates, which are like a mollusk radula (a toothed ribbon of teeth) or the jaws of an annelid.

The name “Wiwaxia” is derived from the Stoney First Nation Nakota language, meaning “windy.” Although, Wiwaxia has been found (mostly as disarticulated scales) at various localities in the world (e.g., China), its principal locality is the Burgess Shale.