Seashell

Seashell is the protective exoskeleton produced by mollusks—animals like snails, clams, oysters, and scallops. Made mostly of calcium carbonate, shells grow layer by layer as the mollusk secretes minerals from a specialized tissue called the mantle. Shell shapes vary from spiral cones to smooth fans, each adapted to the animal's lifestyle.

Gastropods (snails) carry single coiled shells they can retreat into when predators approach or tides recede. Bivalves such as clams and mussels have two hinged halves that close tightly for defense. Some mollusks, like squids and nudibranchs, have reduced internal shells or none at all.

Shell color and pattern come from pigments laid down during growth. Bands, spots, and ridges may help camouflage the animal or strengthen the shell. As the mollusk grows, the shell expands outward from the opening, leaving growth lines similar to tree rings.

After the mollusk dies, empty seashells often wash onto beaches. Collectors and scientists study them to learn about biodiversity, water quality, and ancient trade. Archaeologists find shell jewelry and tools at historical sites, showing how people have valued shells for thousands of years.

Healthy shell populations depend on clean, balanced oceans. Acidifying waters dissolve calcium carbonate, making it harder for mollusks to build strong shells. Conservation efforts include reducing pollution, protecting seagrass beds and reefs where young mollusks grow, and monitoring shells for signs of changing ocean chemistry.