Polyplacophora means "many plates". The plates refer to the shell, which is made of aragonite, a calcium carbonate mineral. The shell is quite flexible, and the chiton can even roll into a ball. The chiton has eight plates, and underneath the plates is a muscular foot that moves the chiton over rocks and other structures, both in and out of the water. It also has a tongue-shaped structure called the radula, which has many rows of 17 teeth each. Some use it to scrape algae off rocks, while others are carnivorous, catching tiny zooplankton and other small animals that live in shallow water.