What Are Seashells A seashell is a hard, protective exoskeleton formed by invertebrate animals who live in the sea and are often found washed up on beaches throughout the world. The most common animals which produce a seashell are mollusks, crabs, oysters, barnacles, brachiopods, annelid worms, and sea urchins. While most seashells are external, some … Continue reading Seashell