We humans have skeletons on the inside of our bodies, with muscles attached to the bones. The crab has its skeleton on the outside, in the form of a shell. The crab's shell helps to protect it, like a suit of armour. As long as it is wearing its armour, the crab cannot grow. It has to get rid of its shell, and grow a new one, in order to get bigger. | | Crabs and lobsters have tough shells that help to protect them. |
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