Balanus nubilus

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), and containing the largest known muscle fibres.

Balanus nubilus is a northeast Pacific species that ranges from southern Alaska to Baja California. It is frequently found growing on rocks, pier pilings and hard-shelled animals at depths of up to 90 m (300 ft). Like other acorn barnacles, B. nubilus is a filter feeder; it, in turn, is sometimes eaten by sea otters, sea stars, crabs and the Native Americans of the Pacific Northwest. Abandoned shells of B. nubilus are used by the crab Glebocarcinus oregonensis for shelter.