Lynne Thompson, age 7s of Lake Jackson, Texas, for her question:

How are ,sea: shells made?

Sea shells are made mostly of carbonate of lime. Marble, chalk, and limestone are also composed of this mineral. This is not surprising because marble, chalk and limestone are made from the shells of countless little sea creatures. Sea water is rich in these limy compounds because they are soft minerals. The running streams dissolve them from the rocks and rush down to dump them in the ocean.

Shells are made by mollusk animals and there; are more than 70,000 different mollusks living in our world. Slugs, squids and octopuses are mollusks without shells; But the average mollusk builds himself a fortress of limy minerals. Each kind of mollusk builds his own kind of house, a perfect copy of the houses built by his mother and his father.

Mollusks are soft‑bodied creatures, with no teeth or claws to defend themselves. They cannot attack. They can only hide from their enemies in their shell fortresses. The empty sea shell you find on the shore was made by a soft mollusk to defend himself from his enemies.

Collecting sea shells is called conchology. A collector can assemble and classify a great variety of shells from all over the world. Each shell has its own beauty of form and usually of color, Yot every mollusk uses the same method to construct his shell.

The soft mollusk body is wrapped in a loose skin called the mantle. Water, rich in minerals, is constantly flowing through this body. Special cells in the mantle select the limy minerals from the water. They ooze or secrete a tacky material which hardens into shell. These cells in the mantle work as long as the mollusk lives. So the shell is constantly growing in size or thickness.

Conchologists divide the vast number of sea shells into a number of classes. I"~ beginner starts out with two broad divisions clearly in his mind. One is the group of shells called univalves. The other is the group called bivalves. The valve part of these words is coined from an older word meaning a door. The conche and the cowrie are good. examples of univalves. The univalvos are the mollusks enfolded in a one‑piece shell. The bivalves are enfolded between two shells hinged together with a strong muscle. The clam and the oyster are good examples of bivalves„

If you are a collector make sure each specimen is labeled with its name and place of origin: Raid your library for detailed information and, when you go shell hunting, be sure to collect several specimens of each variety. Your collection will grow as you swap these extras for specimens that you do not have.