Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Cirripedi (barnacles)

GENERAL CHARACTERISTICS: Free-living barnacles are attached to the substratum by cement glands that form the base of the first pair of antennae; in effect, the animal is fixed upside down by means of its forehead. Inside the carapace, the animal lies on its back, with its limbs projecting upwards. There are six pairs of thoracic limbs, referred to as “cirri”, which are feathery and very long, being used to filter food from the water and move it towards the mouth. They have no gills, absorbing oxygen from the water through their limbs and the inner membrane of the carapace. The excretory organs of barnacles are maxillary glands.


DISTRIBUTION/HABITAT: They are also found in all the world’s oceans as hitchhikers on ships, driftwood, and other living animals such as whales, crabs, mollusks, and turtles.

DIET IN THE WILD: Rhythmic movement of the appendages captures small animals, organic fragments, and other suspended nutrients.

PREDATORS: the most common predators on barnacles are whelks. They are able to grind through the calcareous exoskeletons of barnacles and feed on the softer inside parts. Mussels also prey on barnacle larvae. Another predator on barnacles is the starfish species Pisaster ochraceus.

REPRODUCTION: Barnacles begin life as a free-swimming larva. Upon settling, the animal attaches to a hard substrate by its head end. Overlapping plates of calcium carbonate are then secreted externally and protect the animal from predators and water loss.

REMARKS: Various barnacle species create serious and expensive fouling problems on ship hulls and pilings. In two years, 10 tons of barnacles may attach to a large tanker, causing huge losses in fuel efficiency.

Since the intertidal zone periodically desiccates, barnacles are well adapted against water loss. Their calcite shells are impermeable, and they possess two plates which they can slide across their aperture when not feeding. These plates also protect against predation.



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