Armilimax pauljamisoni n. gen. n. sp.
Middle Cambrian
Spence Shale Member, Langston Formation
Wellsville Mountains, Box Elder County, UT

26mm x 23mm halkieriid on 173mm slab.

Halkieriids are strange, slug-like animals with a mollusc-like shell capped on one or both ends, but they aren’t molluscs. Most modern analyses place them in a group related to the famous Burgess Shale taxon Wiwaxia because their bodies are typically covered with scale-like sclerites. The cap shells were among the first fossils of halkieriids found and it was assumed they were either mollusc or brachiopod shells. You can imagine that when the very first whole animals were found it was quite a surprise to discover that these shells were actually a sort of armored sclerite from a very alien animal.

Until recently, complete halkieriids were only known from a few extraordinary fossil lagerstatten like the Sirius Passet Fauna in Greenland so finding a complete halkieriid in the United States is a very special discovery. Armilimax was only first discovered in 2020 so study of this strange animal is still ongoing.

The paper describing it can be found here: Armilimax description (paywalled unfortunately)

See also: Wikipedia – Armilimax