A barnacle is a type of arthropod belonging to infraclass Cirripedia in the subphylum Crustacea and is hence distantly related to crabs and lobsters. Some authorities regard Cirripedia as a full class or subclass, and the orders listed at right are sometimes treated as superorders. Around 1,220 barnacle species are currently known.
Barnacles have two larval stages. The first is called the nauplius, which spends its time as part of the plankton, floating wherever the wind, waves, currents, and tides may take it, whilst eating and molting. This lasts for about two weeks until the sixth stage is reached. At this point the nauplius metamorphoses into a non-feeding, more strongly swimming cyprid larva. The cyprids settle down in an area where environmental cues indicate a safe and productive environment. If they don't, the larvae will die.
When an appropriate place is found, the cyprid larva cements itself headfirst to the surface and then undergoes metamorphosis into a juvenile barnacle. Typical barnacles develop six hard armor plates to surround and protect their body. For the rest of their lives they are cemented to the ground, using their feathery legs to capture plankton and gametes when spawning. They are usually found in the intertidal zone.
Like many invertebrates, barnacles are hermaphroditic and alternate male and female roles over time.
Barnacles often attach themselves to human-made structures, sometimes to the structure's detriment. In particular to ships, they are classified as fouling organisms.
However, some members of the class have quite a different mode of life. For example, members of the genus Sacculina are parasitic on crabs.
- Rock barnacle at Aquascope
- Barnacles from the Marine Education Society of Australasia
"Barnacles" is also a phrase used in SpongeBob SquarePants, usually said when something bad has happened or is about to happen.
The Barnacle Goose gets its name from the ancient European belief that it grew from the gooseneck barnacle, Pollicipes polymerus; eggs and goslings of this bird were never seen because it bred in the remote Arctic. Since barnacles are seafood, the Barnacle Goose was counted as a fish, and could be eaten by Catholics on Fridays, when meat used to be forbidden.