Polyplacophora is a class of marine mollusks commonly known as chitons. They are characterized by their eight overlapping calcareous plates on their dorsal side, which provide protection. Chitons have a broad, flat body that allows them to cling tightly to rocky surfaces in intertidal zones. These creatures have a unique feeding structure called a radula, which they use to scrape algae and other food from rocks. Chitons are primarily found in shallow waters, and they play an important role in their ecosystems by contributing to the grazing of algae and maintaining the balance of marine habitats.