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Scientific classification

A barnacle is a type of arthropod, in the subphylum (or class: classification schemes differ) Crustacea and as such distantly related to the crabs and lobsters. However, barnacles are in the class Cirripedia. Some authorities regard this as a subclass or infraclass, and the orders listed at right are sometimes treated as superorders. There are around 1,220 barnacle species currently known.

Barnacles spend their early life as part of the plankton, floating wherever the wind, waves, currentss, and tides send them, surrounded by a bivalve shell. They then settle down in an area where environmental cues indicate is a safe and productive environment. Typical barnacles stick their legs in the air, and develop six hard plates to surround the body. For the rest of their lives they are cemented to the ground, using the feathery legs to capture plankton and gametes when spawning. They are usually found in the intertidal zone.

Since barnacles often attach themselves to human-made structures, sometimes to their detriment, and in particular to ships, they are classified as fouling organisms.

However, some members of the class have quite a quite different mode of life. For example, members of the genus Sacculina are parasitic on crabs.

The Barnacle Goose gets its name from the ancient European belief that it grew from the bivalve (eggs and goslings of this species were never seen because it bred in the remote Arctic). As such, it counted as a fish, and could be eaten by Catholics on Fridays, when meat used to be forbidden.