The skeleton is the supporting structure of an organism. There are three different types of skeletons: hydrostatic skeletons, endoskeletons and exoskeletons.
- Hydrostatic skeleton: Water exerts pressure on muscular walls, for example, in jellyfish.
- Exoskeleton: The stable chitinous or mineralised outer shell of an organism, for example, the shell of a grasshopper or prawn.
- Endoskeleton: A cartilaginous or mineralized support structure inside the body, for example, in humans and other vertebrates.
As you will learn in another tutorial on History of Life on Earth, many of these structural adaptations allowed animals to move from water onto land.