pen shell
Quick Summary
A pen shell is a type of bivalve mollusk belonging to the family Pinnidae. Its shell is shaped like a quill pen. These mollusks have unique defense mechanisms; for instance, the fan shell, a type of pen shell, can secrete sulfuric acid when threatened. Bivalves, in general, are mollusks with shells divided into two valves. They inhabit various environments and have shells adapted for defense, burrowing, or attachment. Mollusks reproduce sexually, releasing eggs and sperm into the water or through internal fertilization, and many develop through larval stages before becoming adults.1234
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