According to BBC, an endoskeleton is a bone structure located in the interior of an animal, and an exoskeleton is a bone structure located on the exterior of an animal. Each type of skeleton has unique advantages and disadvantages in helping the animal survive.
Some animals, like jellyfish and worms, do not have a skeleton. Their bodies, therefore, are more susceptible to damage from predators or the environment. Skeletons can be internal or external and aid in functions like movement and muscular development. Endoskeletons exist on the inside of an animal. They are less protective than exoskeletons, but they are able to support heavy weights and sizes while remaining lightweight. Another advantage of endoskeletons is that they grow as the organism grows in size. An animal with an endoskeleton never has to undergo molting, or bone shedding. Humans, dogs and fish are examples of animals with endoskeletons.
Exoskeletons exist on the outside of an animal. This skeleton serves as a hard outer coating that helps protect the animal from predators and the environment. This outer coating is made from a durable substance called chitin. The exoskeleton covers the muscles and soft tissue of the animal, providing better leverage for muscular movement. As the animal increases in size, however, the exoskeleton becomes too heavy and restricts growth. Thus, the exoskeleton must be shed and regrown. This molting process takes place various times over the lifetime of the animal. Insects, crustaceans and arachnids are examples of animals with exoskeletons.