Barnacles are crustaceans like crabs and lobsters. Are you surprised? Your first impression is that they certainly don't look like their relatives, but if you look at the internal anatomy you'll find they have jointed appendages like a crustacean. Barnacles live their adult lives permanently attached to the rock face. They rely on the tide to bring them food. They have a watertight shell with a moveable top that they can open and close to gather food. When the tide is out, they tightly close their shell keeping some water inside their shell.