(class Amphineura, subclass Polyplacophora)
An order of polyplacophorans, some of which have the articulamentum present as insertion plates. Advanced forms possess a mesostracum layer to the valves. They first appeared in the Carboniferous. The suborder Acanthochitonina includes the largest of all polyplacophorans, although some of its members are small.
Subjects: Zoology and Animal Sciences.