section_path: Classification/Exoskeletons
section_name: Exoskeletons
paragraph_text: Exoskeletons
  
  An exoskeleton is an external skeleton that covers the body of an animal, serving as armor to protect an animal from predators. Arthropods have exoskeletons that encase their bodies, and have to undergo periodic moulting or ecdysis as the animals grow. The shells of molluscs are another form of exoskeleton. Exoskeletons provide surfaces for the attachment of muscles, and specialized appendanges of the exoskeleton can assist with movement and defense. In arthropods, the exoskeleton also assists with sensory perception.
  
  An external skeleton can be quite heavy in relation to the overall mass of an animal, so on land, organisms that have an exoskeleton are mostly relatively small. Somewhat larger aquatic animals can support an exoskeleton because weight is less of a consideration underwater. The southern giant clam, a species of extremely large saltwater clam in the Pacific Ocean, has a shell that is massive in both size and weight. Syrinx aruanus is a species of sea snail with a very large shell.