A striped barnacle inside of its hard shell. By Auguste Le Roux
Young barnacles, called larvae, swim freely through water in the ocean. When a barnacle reaches the right age, it attaches itself to a hard surface, grows a shell around most of its body, and stays put for the rest of its life. Striped barnacles often choose a rock or mangrove tree root on the edge of the ocean. They stay in the same location for their entire lives. Other barnacles choose a ship bottom, a whale, or the shell of a snail or other animal that moves around.
Barnacles are filter feeders that collect their food from the water around them. A barnacle sticks its legs out of the opening in its shell and uses them to grab tiny plants called plankton that drift in ocean currents. The barnacle sweeps the food into its mouth and sticks it legs out over and over again to gather food.
Barnacles that attach to rocks or tree roots often choose the intertidal zone for their home. The intertidal zone is an area on the ocean shore that is covered by water when the tide is high and exposed to the air when the tide is low. Barnacles can only feed when they are underwater, so they stay inside their shells when the tide is low.
When they are underwater, barnacles stick their legs out to gather tiny plants called plankton. By Kim Hansen
Barnacles sometimes grow together in large groups called colonies. By Zephyris
The above link plus:
Andrew, Campbell C. Seashore Life. New York: Exeter Books, 1983. Pp. 44-45.
Kaplan, Eugene H. A Field Guide to Southeastern and Caribbean Seashores. Houghton Mifflin Company: Boston, 1988. Pp. 293-300.