Oysters are mollusks found in the warm coastal waters of all oceans.

An oyster is a type of shellfish. It lives in a rough, hinged shell. As soon as an oyster is threatened, it tightly closes its shell to protect itself from enemies. It also closes its shell when it is out of the water for a long time. The oyster opens its shell 12 millimeters to feed.

Algae often grow on the sells of oysters like this thorny oyster.