Cabrillo Marine Aquarium

Acorn Barnacle

Balanus spp.


Fun Facts

    Barnacles are hermaphroditic (they have both female and male sex organs).

    Barnacles use their feathery feet, called cirri, to both feed and breathe.




Acorn barnacles are filter-feeding crustaceans that live attached to hard surfaces of rocks in the intertidal zone. They are small, about 1-2 cm in diameter, and are whitish to gray in color.

During the spring and summer, planktonic larvae settle onto a rock. They then “glue” their heads to the hard rocky surface. Cement glands within the antennae produce the brown glue that fastens the barnacle to the surface. During the winter and spring, they brood fertilized eggs within their shells. Depending on the size of the parent, 1,000 to 30,000 nauplius larvae are produced per brood.
To learn more about acorn barnacles and their relatives visit the Rocky Shores Room at the Aquarium.