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"Cirripedia" from Ernst Haeckel's Kunstformen der Natur (1904). The crab at the centre is nursing the externa of the parasitic cirripede Sacculina
"Cirripedia" from Ernst Haeckel's Kunstformen der Natur (1904). The crab at the centre is nursing the externa of the parasitic cirripede Sacculina
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Maxillopoda
Subclass: Thecostraca
Infraclass: Cirripedia
Burmeister, 1834


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. The name "Cirripedia" means "curl-footed".

Barnacles were first fully studied and classified by Charles Darwin, at the suggestion of his friend Joseph Dalton Hooker, in his quest to further his ongoing development of the theory of evolution and natural selection.

Life cycle

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 second 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.

Balanus balanoides
Balanus balanoides

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 bodies. 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.

Once metamorphosis is over and they have reached their adult form, barnacles will continue to grow, but not molt. Instead, they grow by adding new material to the ends of their heavily calcified plates.

Like many invertebrates, barnacles are hermaphroditic and alternate male and female roles over time. Barnacles have the longest penis in the animal kingdom, in proportion to their body length .

Barnacles often attach themselves to man-made structures, sometimes to the structure's detriment. Particularly in the case of 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.

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.


Balanidae, Mission Beach National Park, Queensland, Australia, 2002
Balanidae, Mission Beach National Park, Queensland, Australia, 2002
Corrosion caused partly by barnacles
Corrosion caused partly by barnacles

This article follows Martin and Davis in placing Cirripedia as an infraorder of Thecostraca and in the following classification of cirripedes down to the level of orders:

Infraclass Cirripedia Burmeister, 1834

  • Superorder Acrothoracica Gruvel, 1905
    • Order Pygophora Berndt, 1907
    • Order Apygophora Berndt, 1907
  • Superorder Rhizocephala Müller, 1862
    • Order Kentrogonida Delage, 1884
    • Order Akentrogonida Häfele, 1911
  • Superorder Thoracica Darwin, 1854
    • Order Pedunculata Lamarck, 1818
    • Order Sessilia Lamarck, 1818


Other names for this group of crustaceans include Thyrostraca, Cirrhopoda (meaning "tawny-footed"), Cirrhipoda, and Cirrhipedia.

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