was first described in 1899 from a single spine found across the
valley from the Burgess Shale, where complete specimens were subsequently
discovered. The slug-appearing animal had two rows of spines along
the back, ostensibly affording some protection from predators. The
remainder of the upper (dorsal) body was covered with small, flat,
overlapping hard plates, termed sclerites. Each of these little
scales was attached with a root-like base and it is assumed Wiwaxia
grew by molting the plates.
Because of the sclerites, some researchers have attempted to place
Wiwaxia with the annelids,
and indeed, it may be ancestrial or closely related to the segmented
worms. The polychaete annelid worms are spiny with chaetae that
there are none on the bottom (ventral) surface, the animal partly
resembles the slug, a member of the mollusk family. However, mollusks
do not have any sclerite armor so the animal's affinity to present
day species is unsettled. It did have an anterior jaw with two rows
of teeth on the ventral surface, suggesting it was a bottom feeder.
Fossil sizes range from 6 to 50 mm. The animal is rare with but
140 specimens known from the Burgess Shale.
is likely that trilobite collectors in Utah have discarded many
Wiwaxia and other soft-bodied animals over the years. The material
is harder to see than trilobites and many local collectors were
simply unfamiliar with soft-bodied animals and didn't recognize
what they were. Nonetheless, these animals are as rare as they are
hard to see in the Marjum Formation.
See: Utah Cambrian
Explosion Fossils Cambrian Explosion