Giant Acorn Barnacle    Balanus nubilus

One of the largest barnacles in the world the Giant Acorn barnacle occurs in the subtidal zone through out Puget Sound.  This dried specimen is a around four inches in diameter, but could have grow to 6 inches across and 3 inches  high.  It lives under docks or on rocks in the extreme low tide area or most commonly in deep water to a depth of around 300 ft.  It is distributed from southern Alaska to southern California.

The opening of the volcano-like shell is where the feeding appendages emerge.  The appendages are modified legs. An old marine biologist saying is that “barnacles are like shrimp which have laid on their backs, surrounded themselves with a shell for protection and make a living by kicking food into their mouths”.

Giant barnacles can occur singly or in large groups forming large reef-like structures.  The large muscle of the barnacle has been used by scientists for investigation of muscle biology and chemistry.

They are eaten by sea stars and crabs.  Empty shells are used as hiding places for a variety of animals including small fish who use them as a nursery.

See a video of the Giant Acorn Barnacle filmed by Phil Sconce on youtube