Late Cambrian

Weeks Shale Formation

House Range, UT, USA

20mm wide (43mm if uncurled) palaeoscolecid on 72mm slab

Worm.

We think of all worms belonging to the same group but the word “worm” is actually a catch-all for a diverse mix of animals representing more than one phylum – more than one ancestry.  Some worms have had jaws or armor (composed of sclerites) but most haven’t so they appear in the fossil record only where other soft-bodied organisms are preserved.

Palaeoscolex is a worm known from isolated sclerites at some localities but from occasional body impressions in a few others. This may be the only occurrence in North America – otherwise known from the Cambrian of Russia and China.