Why is the exoskeleton vital to the animals movement?

Exoskeletons contain rigid and resistant components that fulfil a set of functional roles including protection, excretion, sensing, support, feeding and (for terrestrial organisms) acting as a barrier against desiccation. Exoskeletons have a role in defence from predators, support, and in providing a framework which musculature can attach to. Exoskeletons contain Chitin and when calcium carbonate is added, the exoskeleton grows in strength and hardness.