A barnacle is a type of marine crustacean belonging to the class Cirripedia. These animals are known for their distinctive hard shell, which adheres firmly to various surfaces, including rocks, ships, and even the shells of other sea creatures. Barnacles are sessile, meaning they remain fixed in one place throughout their adult lives. They primarily feed by filtering plankton and other particles from the water using their specialized appendages. Despite their seemingly simple structure, barnacles are fascinating creatures that play an important role in marine ecosystems and can also impact marine industries due to their hardiness and adhesive nature.