Balanus nubilus, commonly called the giant acorn barnacle, is the world's largest barnacle, reaching a diameter of 15 cm (6 in) and a height of up to 30 cm (12 in),[3] and containing the largest known muscle fibres.

[4][5] Balanus nubilus is a northeast Pacific species that ranges from southern Alaska to Baja California.

[6] It is frequently found growing on rocks, pier pilings and hard-shelled animals at depths of up to 90 m (300 ft).

[4] Like other acorn barnacles, B. nubilus is a filter feeder; it, in turn, is sometimes eaten by sea otters,[7] sea stars, crabs[8] and the Native Americans of the Pacific Northwest.

[9] Abandoned shells of B. nubilus are used by the crab Glebocarcinus oregonensis for shelter.