1001 Space Earth Nature Evolution Fossils and Prehistoric Life Dinosaurs Simple Animals Insects and Spiders Fish Amphibians Reptiles Birds Sea Mammals Land Mammals Plant Kingdom How Plants Live Unusual Plants Ecology Conservation Animal Behaviour Pets and Farm Animals History Human World Science and Technology

Choose a Page:What use is a skeleton?What shape is an amoeba?What is inside an earthworm's body?What is coral made from?Why do scorpions dance?How many legs does a centipede have?What colour is a worm's blood?Why do squid change colour?Why does a sea urchin have spines?*Why does a crab have a shell?*How do you get ink from an octopus?How does a cone shell hunt?Are sea anemones animals or plants? Why does a crab have a shell? 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.   Previous: Back Book: 1001 Section: Nature Chapter: Simple Animals