Rock barnacles are a type of marine invertebrate that attach themselves to rocks and other hard surfaces using a strong, glue-like substance. Synonyms for rock barnacle include acorn barnacle, gooseneck barnacle, and volcano barnacle, based on their physical appearance. They are also referred to as sessile crustaceans, meaning that they remain fixed in one place for their entire lives. Rock barnacles have a hard, calcareous shell that helps protect them against predators and harsh environmental conditions. They are an important part of marine ecosystems, providing shelter and food for other organisms. Despite their small size, rock barnacles play a crucial role in the marine food chain and contribute to the overall health of coastal habitats.