The true limpets (subclass Patellogastropoda) mostly live in the intertidal zone. They possess flattened cone-shaped shells that are open to the bottom, allowing the animal to clamp its shell down to the rock, both for defence, and to "lock in" water, allowing intertidal limpets to breathe during low tide. They are able to clamp down so hard that it is very difficult to remove them without killing the animal, so care should be taken not to handle them.