What is Barnacle?
{{Taxobox | color = | name = Barnacles | image = Semibalanus balanoides upernavik 2007-07-05.jpg | image_width = 250px | image_caption = Barnacles under water, showing the 'feet' in action | regnum = [[Animal]]ia | phylum = [[Arthropod]]a | subphylum = [[Crustacean|Crustacea]] | classis = [[Maxillopoda]] | infraclassis = '''Cirripedia''' | subdivision_ranks = [[Order (biology)|Orders]] | subdivision = * '''Superorder Thoracica''' ** Sessilia ** Pedunculata * '''Superorder Rhizocephala''' ** Akentrogonida ** Kentrogonida }} [[File:Shrimp nauplius.jpg|thumb|right|250px|Nauplius larva of a [[copepod]]]] [[File:Balanus improvisus, nauplius.jpg|thumb|right|250px|Nauplius larva of a cirripede]] [[File:Balanus improvisus, cypris.jpg|thumb|right|250px|the second stage larva of a barnacle, the ''Cypris''.]] A '''barnacle''' is a '''cirripede''', a kind of [[crustacean]]. It is covered with hard plates of [[calcium carbonate]], and lives stuck to hard surfaces. It does not look like a crustacean, and for many centuries it was thought to be a [[mollusc]]. In the 1830s, J.V. Thompson found their [[larva]]e, and followed their development through to their adult form. They have a [[nauplius]] larva, typical of crustaeans.<ref>Thompson J.V. 1830. On the cirripedes or barnacles; demonstrating their deceptive character; the extraordinary metamorphoses they undergo, and the class of animals to which they indisputably belong. ''Zoological Researches'', memoir 4, Riding, Cork.</ref><ref>Thompson J.V. 1835. Discovery of the metamorphoses in the second type of cirripedes, viz., the Lepades, completing the natural history of these singular animals, and confirming their affinity with the Crustacea. ''Philosophical Transactions of the Royal Society of London''. 335&ndash;9</ref> Later [[Charles Darwin]], who spent eight years working on barnacles, found that Thompson had been right.<ref>Darwin, Charles. 1851: ''A Monograph of the Sub-class Cirripedia, with figures of all the species. The Lepadidae; or, Pedunculated Cirripedes''. Liv