Collecting beach shells is a common hobby among ocean lovers. Shells come in many shapes, sizes, and colors. Seashells come from animals that live in the ocean, known as mollusks. Mollusks are invertebrates that do not have an internal skeleton. These invertebrates use the shells as protection. A mollusk lives inside its shell, taking it wherever it goes. When the mollusks dies or grows out of its shell, the shell sinks to the ocean floor and lies vacant until another inhabitant claims it, or it washes up on the beach shore.