Subclass of Amphineura (or in some classifications ranked as a molluscan class) in which seven or eight dorsal plates, generally composed of calcium carbonate, are enclosed by a marginal girdle. The plates articulate with one another and overlap to a varying extent. The anterior and posterior plates differ from the others, the anterior plate often being ribbed. Polyplacophora are entirely marine, and first appeared in the Upper Cambrian.
Subjects: Zoology and Animal Sciences — Earth Sciences and Geography.