How are clams shells created?

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How are clams shells created?
Molluscs have a mantle, which is a fold of the outer skin lining the shell, and a muscular foot that is used for motion. Many molluscs have their mantle produce a calcium carbonate external shell.

The shell will grow over time as the animal inside adds its building material to the leading edge near the opening. This causes the shell to become longer and wider to better accommodate the growing animal inside. A mollusc shell is formed, repaired and maintained by a part of the mollusc called the mantle. Injuries to or abnormal conditions of the mantle are often reflected in the shell they form and tend. When the animal encounters harsh conditions which limit its food supply or otherwise cause it to become dormant for a while, the mantle often ceases to produce the shell substance. When conditions improve again and the mantle resumes its task, a "growth line" which extends the entire length of the shell is produced, and the pattern and even the colors on the shell after these dormant periods are sometimes quite different from previous colors and patterns. Interestingly, each species of mollusc animals will build the external shell in specific shape, pattern, ornamentation, and color.

Shells are composite materials of calcium carbonate, found either as calcite or aragonite and organic macromolecules, mainly proteins and polysaccharides.

Nacre (also known as mother of pearl, a naturally-occurring organic-inorganic composite) is secreted by the epithelial cells (formed by the germ layer ectoderm) of the mantle tissue of certain species of mollusk. Mollusk blood is rich in dissolved calcium. In these mollusks the calcium is concentrated out from the blood where it can crystallize as calcium carbonate.

Mollusc shells (especially those formed by marine species) are very durable and outlast the otherwise soft-bodied animals that produce them by a very long time (sometimes thousands of years). They fossilise easily, and fossil mollusc shells date all the way back to the Cambrian period. Large amounts of shells may form sediment and become compressed into limestone.
Reply:their parent clam dna is embedded in special minerals they secrete and after the shell finishes forming from the minerals duplicating over and over the clam inside uses the dna and begins to grow.
Reply:The clam spawn is very, very tiny, and it builds a shell around itself. As it grows larger, it adds to the shell. If you look carefully, you will see the growth ridges that accrue when when shell is enlarged.

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