Why do clams have shells?
For grown-ups: the science
Clams have hard shells to protect their soft bodies while they live in water.
Clams are bivalve mollusks with soft bodies enclosed by two hinged shell valves. Their calcium carbonate shells provide protection and support, while the animal can open the valves for feeding, breathing, and movement. Shell closure reduces access by many predators, though it is not complete protection.
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Transcript
A clam rests under the sandy water. Why does it wear a hard shell?
A clam has a soft body, with no bones around its outside. Its shell is a hard cover that helps protect its soft parts.
When trouble comes near, the clam pulls its body inside and closes its two shell halves. The closed shell makes it harder for many animals to reach it.
The clam can open a little to let water flow through. It takes food and oxygen from the water, then closes again when it needs to.
So, a clam's shell is a strong home it carries around. It helps keep its soft body safer while it lives in water.