Balanus is a genus of barnacles, which are small marine crustaceans that attach themselves to hard surfaces in the ocean, such as rocks, ships, and even other animals. They have a hard outer shell made of calcium carbonate, which protects them from predators and environmental conditions. Balanus species are filter feeders, using their specialized appendages to capture plankton and other small particles from the water. These barnacles are commonly found in intertidal zones, where they can withstand varying levels of water exposure. Balanus plays an important role in marine ecosystems, providing habitat for other organisms and contributing to the overall biodiversity of coastal environments.