Balanus nubilus

Balanus nubilus, commonly called the giant acorn barnacle, is the world's largest barnacle, reaching a diameter of 15 centimetres (5.9 in) and a height of up to 30 centimetres (12 in), and containing the largest known muscle fibres.

Balanus nubilus is frequently found growing on rocks, pier pilings and hard-shelled animals at depths of up to 90 metres (300 ft) from Alaska to La Jolla, San Diego County, California. 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.