Barnacles are sessile crustaceans that live in large populations along the shoreline. They have a hard conical shaped shell which is made up of overlapping plates. They are able to glue themselves to different substrates such as wood, rock, and boats etc. where they live a sedentary lifestyle. Barnacles are able to open their shells allowing them to expose their fan shaped limbs known as cirri. These move rhythmically in the water sweeping up suspended food particles in a sieve like fashion. When disturbed they will quickly withdraw their limbs back into their shells to avoid any potential danger. The common barnacle is up to 2cm in diameter.