The skeletal system provides support, protection, movement, and shape to the human body and other animals. There are three main types of skeletal systems - endoskeleton, exoskeleton, and hydrostatic skeleton. An endoskeleton is found in vertebrates and consists of bones or cartilage inside the body. An exoskeleton is an external shell like in insects and crustaceans. A hydrostatic skeleton uses fluid pressure, found in some invertebrates. The skeletal system allows vertebrates and invertebrates to survive on land and in water.