Shells are hard, protective outer coverings created by various animals, primarily mollusks like snails and clams. They serve as a defense mechanism against predators and environmental hazards. Shells are made of calcium carbonate or other materials, and they come in various shapes, sizes, and colors, reflecting the species that produced them. In addition to mollusks, other creatures like turtles and crustaceans also have shells. These structures can provide buoyancy, camouflage, and even a habitat for other organisms. Shells play a crucial role in the ecosystem, contributing to the nutrient cycle and serving as a source of food for some animals.