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Barnacles are small crustaceans that are arthropods and closely related to the blue crab.

They are found attached to hard surfaces such as rocks, pilings, grasses, boat bottoms and even oysters and clam shells. They can tolerate an variety of conditions from high salinity at the inlets to the bay to nearly fresh water. 

Barnacles vary in color from gray to white and in size from less than half an inch to 1 inch in diameter.


There are two major groups of barnacles:

Acorn barnacles (Family - Balanomorpha) attach directly to a firm surface.  Some species of acorn barnacles are a common in Barnegat Bay, covering rocks and other stationary objects. When the tide is in, they open their shell-like cases and use their legs to catch particles in the water column.

Goose barnacles (Family - Lepadomorpha) typically live in the ocean and attach to floating objects by a long rubbery stalk - sometimes called "goose-neck" barnacles.

Acorn barnacle species live in intertidal regions and are exposed to the air for a significant part of each day.

Their body is a shell of six overlapping plates of calcium carbonate with a gap at the top covered by valve that open when the animal is submerged, and close when it is exposed to the air.

     <click on image to enlarge>

The base of this igloo-like structure attaches to a firm surface such as a pier, rock, or the hull of a boat. When the tide is low, the barnacle closes its valves to retain moisture and does not emerge from its "igloo" until it is again submerged, at which time six pairs of feathery, chitinous legs called cirri emerge and sweep planktonic material (its source of nourishment) into its cavity.

Barnacles are formed by six overlapping plates of shell with a flat base and an opening at the top. The top opening has two valves that open and close for the barnacle to feed.

Barnacles vary in color from gray to white and in size from less than half an inch to 1 inch in diameter.


Bay barnacle                   Balanus improvisus

The bay barnacle is white, about 1/4 inch high and 1/2 inch wide, similarly constructed, preferring to attach to rocks, pilings oyster shells and other hard-shelled animals in brackish estuaries, in a wider range of depths, from shallow water to 120 feet deep