All mollusks build their own shells, whether they live in water or on land. Creatures like snails, clams, oysters and mussels use an organ called a mantle to secrete layers of calcium carbonate, which ...

Snails have shells the moment they're born, but it's kind of hard to tell. In fact, it's hard to even see a baby snail. Some are nearly microscopic, such as Angustopila psammion, whose adult-sized ...