<p>Molluscs are actually born with their shells. When they are born, the shells are tiny, soft and very fragile. So to make it stronger, the newborn molluscs go out looking for a calcium diet. Most start with their egg shells. It's easy and the first thing available so they eat it and digest the calcium.</p><p>As the molluscs grow, they continue to produce the soft material of their original shell and this pushes out the old harder shell before solidifying properly. That's why molluscs have what looks like revolutions on them. Its created as they grow bigger, the shells they make get bigger and so the revolutions appear to be getting bigger to. A fully grown molluscs will have its baby shell at the very middle of the revolutions</p>