Shells are hard, protective outer coverings created by various animals, most commonly snails, turtles, and mollusks. These structures serve as a defense against predators and environmental hazards. Shells can be made of different materials, such as calcium carbonate or keratin, and come in various shapes, sizes, and colors, making them fascinating to study and collect. In addition to their protective function, shells also play a role in the animal's growth. As the creature inside grows, it may produce a larger shell, often adding new layers to the existing one. This process allows the animal to adapt to its environment while maintaining its safety within the shell.