Exoskeleton:
* An exoskeleton is a hard, external covering that supports and protects an animal's body.
* It is composed of various materials such as chitin, calcium carbonate, or silica.
* Exoskeletons are found in many invertebrate animals, including insects, crustaceans, and spiders.
* The main functions of an exoskeleton are to:
* Provide structural support and protection for the body.
* Prevent water loss and desiccation.
* Allow for muscle attachment and movement.
* Detect external stimuli, such as pressure and touch.
Shells:
* A shell is a hard, protective outer layer that covers the bodies of certain animals.
* Shells are composed of calcium carbonate, secreted by the animal itself.
* Shells are found in many marine invertebrates, including mollusks (such as snails, clams, and octopuses), brachiopods, and echinoderms (such as sea urchins and starfish).
* The main functions of a shell are to:
* Provide structural support and protection for the body.
* Prevent water loss and desiccation.
* Provide buoyancy and allow for movement in aquatic environments.
* Act as a camouflage and defense mechanism against predators.
In summary, exoskeletons and shells are both hard, external coverings that provide protection and support for the bodies of animals. However, exoskeletons are found in invertebrates such as insects and crustaceans, while shells are found in marine invertebrates such as mollusks and echinoderms.