Difference between Endoskeleton and Exoskeleton

A skeleton aids in functions like movement and locomotion and muscular development, i.e. it provides structural support to animals, birds, humans, etc., and facilitates movement and locomotion as well as protects the internal organs. It can be internal (endoskeleton) or external (exoskeleton). Some living organisms have an endoskeleton, some have an exoskeleton and some have both. Let us see how an endoskeleton differs from exoskeleton!

Endoskeleton:

It is an internal skeleton present inside the body of a living organism, e.g. a bony or a cartilaginous skeleton of vertebrates. All vertebrates like birds, fish, reptiles, amphibians and mammalians have an endoskeleton. The endoskeleton is the internal support system that provides structural support and protection to the internal organs and aids in the movement and locomotion. Furthermore, it also provides sites for the attachment of muscles and thus can transmit the forces to the muscles.

The endoskeleton mainly comprises bones and cartilage. In some organisms like cartilaginous fishes, it is exclusively made up of cartilage. Bones are made up of bone cells known as osteoblasts and they form joints to articulate with each other. A bone is attached to another bone by ligament and muscles are attached to bones by tendons.

Exoskeleton:

The exoskeleton is the external skeleton that exists on the outside of an organism. It is the hard outer coating that provides support to the body and protects the muscles and soft tissues or organs of the body. It also protects the animal from predators and harsh environment. Exoskeleton develops from the ectoderm. Some common examples of exoskeleton include scales, calcified shells and chitinous cuticle.

Most of the invertebrates or animals that lack backbone have exoskeletons, e.g. grasshoppers, cockroaches and crustaceans like crabs and lobsters. Insects are the largest group in the animal kingdom that has an exoskeleton made up of a substance called chitin. Their wings are attached to the exoskeleton through muscles. Exoskeleton does not grow with the body. It is shed by the insects several times during their life cycle in a process called molting.

Based on the above information, some of the key differences between Endoskeleton and Exoskeleton are as follows:

Endoskeleton	Exoskeleton
It is the internal skeleton present inside the body such as the bony or cartilaginous skeleton of vertebrates.	It is the external skeleton present on the outside of an animal as a hard outer coating.
It is made up of bones and cartilage.	It is made up of scales, chitinous cuticle and calcified shells.
It is found in vertebrates.	It is mainly found in arthropods (insects, spiders, crabs, centipedes, millipedes etc)
It is a living structure that develops from the endoderm.	It is a non-living structure that develops from the ectoderm.
It grows with the body. Animals with endoskeleton do not undergo molting.	It does not grow with the body. It is shed by insects many times in their life cycle in a process called molting.
It provides sites for the attachment of muscles.	It provides an attachment site for the wings through muscles.