The root word "endo-" comes from the Greek word "endon" meaning "inside or within." An endoskeleton is a skeleton that is contained inside the body, and is made up of cartilage and bones. The bones offer support and structure, while cartilage provides cushioning and flexibility. Some vertebrates, such as sharks, have a skeleton that is composed mostly of cartilage. Most vertebrates, including humans, have cartilage that is eventually replaced by bone as the body grows.
In contrast, "exo-" is derived from the word for "external or outside." Animals with an exoskeleton include grasshoppers, cockroaches, lobsters and crabs. Earthworms, jellyfish, starfish and other soft-bodied creatures have a hydroskeleton, also referred to as a hydrostatic skeleton.Learn more about Zoology