An exoskeleton is an outer shell protects and supports the organism. Instead of having an endoskeleton as body support, these organisms have exoskeleton. They are mostly made of chitin which is why they are so stable and hard. This spider is covered by an exoskeleton that is jointed for movement but is not capable of growing or expanding. Because of this, it needs to shed or molt its shell to fit into a larger or stronger one.