Chitons are the most primitive of all living mollusks. They belong to a class called Polyplacophora (bearer of many plates). There lineage extends as far back as the late Cambrian. There are over 430 described species in the fossil record. Almost all  are only  known from individual body plates or valves. The Mazon Creek deposit is one of the only  sites in the world where complete examples have been collected. Modern chitons have changed little from Glaphurochiton concinnus.