Chitons belong to a very old animal group, which exists as far back as the Cambrian (around 500 million years ago). In all those years, it has hardly evolved. It is a slow animal with a raspy tongue. It has eight overlying calcareous plates as shell, which makes them look a lot like pill bugs. If you peel a chiton off from the underground it's attached to, it will roll into a ball just like a pill bug. They use their tongue to scrap algae and even small animals such as bryozoans off of other shells.