seashells

Seashells are the hard, protective outer coverings secreted by many marine mollusks, including gastropods (snails) and bivalves (clams, oysters, mussels). They are primarily composed of calcium carbonate in the crystal forms calcite and aragonite, bound by an organic matrix produced by the mantle. Shells grow by incremental addition as the animal enlarges, often forming spirals in gastropods or two-valued, hinged structures in bivalves.

Shells vary in texture, shape, and color. Outer surfaces may be smooth or sculptured, while inner surfaces are commonly nacreous, or mother-of-pearl, in many species. Pigments and the microstructure of the shell produce a wide range of colors and patterns. Some shells are iridescent, especially the inner layer of many abalones and some other mollusks.

Beyond their protective role, empty shells provide microhabitats for algae, encrusting organisms, and small animals. They also serve as a fossil record for ancient mollusks and as resources for humans, and are often collected for decorative purposes or used in crafts and symbolism.

Humans have used seashells for adornment, jewelry, and tools, and some species have held cultural value as currency. Conch shells are used as horns, while cowry shells have been used as money in various regions and periods.

Environmental concerns include overharvesting, habitat degradation, and ocean acidification, which can reduce mollusks’ ability to form shells. Responsible collecting and conservation measures help maintain mollusk populations and the coastal ecosystems that depend on them.