Barnacles can be found on rocks, sea walls, boat hulls and countless other surfaces in oceans across the world. We usually see them as small, closed mounds resembling beaks, when they are out of the water and closed up to prevent water loss. But when underwater, the barnacle opens up and protrudes many specialised feeding legs called cirri – which also provide the scientific name for barnacles, Cirripedia. What we don’t see is that under their outer shell, barnacles look very similar to shrimps stuck on their backs, as barnacles are crustaceans, too. When they feed on plankton and other organic particles in the water, they rake their hand-like array of cirri through the water, collecting food items on the many little hairs and bristles on their legs and drawing them inside the shell to the mouth.

Image courtesy of Igor Siwanowicz and the Nikon Small World competition.