Pennsylvanian
Francis Creek Shale
Pit 11, Will County, IL, USA
43mm acorn worm

Worm. Mazon Creek. Soft-bodied. Pennsylvanian.

Mazonoglossus is a genus that belongs to the Phylum Hemichordata, the acorn worms. The term “worm” is actually a convenient, if inaccurate, umbrella for a variety of wiggly organisms.  Many belong to the Phylum Annelida, the segmented worms.  A phylum is one of the highest levels of classification, being indicative of a basic body plan – a separate ancestry from other phyla (plural form of phylum).  A starfish has a different basic body plan from a grasshopper so they belong to separate phyla.  Segmented worms are as different from acorn worms as starfish are from grasshoppers.  You just need a biologist to show you how.

Mazonoglossus is known only from the Late Carboniferous of Illinois (Essex fauna of the Mazon Creek Biota). Acorn worms are otherwise almost unknown as fossils but they still live today.