Barnacles are very unusual crustaceans related to crabs and shrimps that are attached to rocky surfaces, docks or pilings.  Barnacles can even be attached to marine mammals like the migrating grey whales of the Pacific Northwest.

These animals are protected by calcareous plates, which form a protective area resembling the shape of a volcano.  The small invertebrate lives inside this space, and has the top entrance covered with another two plates.  These top two plates can be easily opened and closed allowing the barnacle to extend its basket-like feeding limbs (cirri) into the water to collect food.  Basically a barnacle is standing on its head and eating with its feet!  There is also a cement gland on the underside allowing the barnacle to attach itself to a solid surface.

It’s interesting how many barnacles live in the highest intertidal zone and are covered with water for only a few hours each day.  These animals rely on the rushing water flow of high tide to provide them with food particles.  Most of their day is spent hidden in their calcareous home in the hot sun, waiting for the next cooling high tide to arrive.  When exposed to the air during low tide, a barnacle has its two upper plates tightly closed and a small quantity of ocean water stored inside to keep it from drying out; techniques necessary for the animal’s survival.