Has a hard outer shell covering the whole body?

An organism with a hard outer shell covering its entire body is often referred to as having an exoskeleton. This feature is common in many arthropods, such as insects and crustaceans, as well as in some mollusks, like turtles and certain types of snails. The exoskeleton provides protection, support, and aids in locomotion. However, it also requires the organism to molt in order to grow, as the shell does not expand.