Cirripedia is a class of marine crustaceans commonly known as barnacles. They are characterized by their hard, calcareous shells and are often found attached to rocks, ships, and other surfaces in coastal waters. Cirripedes are filter feeders, using their specialized appendages, called cirri, to capture plankton and organic particles from the water. These organisms undergo a unique life cycle, starting as free-swimming larvae before settling down and metamorphosing into their adult form. Cirripedia includes various species, such as Balanus and Lepas, which play important roles in marine ecosystems and can also impact human activities, like shipping and fishing.