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SHELL STRUCTURE

The basic building material of a shell is calcium carbonate, or chalk. With the addition of smaller amounts of other materials to harden it, the shell can grow and protect the mollusk throughout its life. Enveloping the soft living tissues of the mollusk is a membrane called the mantle, which secretes the calcium car- bonate to form the shell itself. Calcium carbonate present in the mollusk’s envi- ronment eventually finds its way into the bloodstream and is then deposited by the mantle onto a tissue called conchiolin, which hardens to form the shell itself. In the living mollusk there is an outer layer called the periostracum, which has the appearance of a brittle, semi-transparent skin. This is added to from the leading

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of senatorial scallops, Mimaclamys sentori— the scallop is a bivalve, with a laterally compressed body and a shell consisting of two valves or movable pieces joined by an elastic ligament.

This living file clam, Lima scabra, uses its sinuous tentacles for both movement and defense. Potential predators are distracted by unpleasant secretions; the clam then makes a swift retreat to safer territory.

Loebbecke’s murex, Pterynotus loe- beckei, lives in 400- to 500-foot-deep (122- to 152-meter-deep) water off the coasts of Japan, Taiwan, and the Philippines. The most striking features are the three waved wings, which are rarely found without some damage. Most shells are a pale orange, but white and pink forms can also be found.

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