Seashells are the former homes of animals called mollusks. Mollusks are small animals that have no backbones. They have delicate and slimy bodies and need shells to protect their fragile bodies from the elements and predators that hunt them.
These mollusks ingest minerals from the water they live in, and secrete a substance known as calcium carbonate. This calcium compound then hardens around the outside of their bodies.
The shell is not actually part of the mollusk’s body but is attached to it. Throughout its life, each mollusk “grows” its shell by continually shedding more calcium carbonate.
The shell is mostly made of calcium and is known as a nacre [ney-ker], meaning “mother of pearl”. It also has an outer layer called a scleroprotein. Scleroproteins are stable, waterproof structures, similar to human fingernails.
The colors and patterns of the many types of mollusks in the world are the result of the many different types of diets available in Earth’s oceans. In warm tropical waters there are more food sources for mollusks and those have more colorful shells, since different foods provide different types of pigments. In cold-water, the mollusks have a more limited food supply and have shells that tend to be solid, darker colors.
When a mollusk dies, it leaves its shell behind, and that is where seashells come from.