Shell

Shells are the hard, protective outer layers created by marine animals, primarily mollusks. They are composed mainly of calcium carbonate, often with some organic components. Shells come in a vast array of shapes, sizes, colors, and textures, reflecting the diversity of the creatures that create them and the environments they inhabit. Their formation involves the secretion of calcium carbonate by the mantle, a tissue layer within the animal. The shell's structure can be simple or complex, with layers that provide strength and protection. Shells are found in oceans, seas, and freshwater environments worldwide, and have been used by humans for tools, decoration, and as a source of food for millennia.