Proplina cornutaformis
Other Mollusc
Lower Ordovician
Gasconade Dolomite
Ozarks, Sullivan, Missouri, USA

Huge 62mm monoplacophoran mollusc. Rare.

Proplina is an early mollusc (Class Monoplacophora) with a cap-like shell from the Late Cambrian to Early Ordovician.  It lived during a time when monoplacophorans and other molluscs were diversifying.

Monoplacophorans disappeared from the fossil record by the end of the Ordovician and were therefore thought to have gone extinct so it was quite a surprise when scientists discovered modern specimens from deepwater environments in 1952.