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The cyprid stage lasts from days to weeks. During this part of the life cycle, the barnacle searches for a place to settle. It explores potential surfaces with modified antennules structures; once it has found a potentially suitable spot, it attaches head-first using its antennules, and a secreted glycoproteinous substance. Larvae are thought to assess surfaces based upon their surface texture, chemistry, relative wettability, colour and the presence/absence and composition of a surface biofilm; swarming species are also more likely to attach near to other barnacles. As the larva exhausts its finite energy reserves, so it becomes less picky in the sites it selects. If the spot is to its liking, it cementing down permanently with another proteinacous compound. This accomplished, it undergoes metamorphosis into a juvenile barnacle.
[edit] Adult stage
Typical acorn barnacles develop six[citation needed] hard calcareous plates to surround and protect their bodies. For the rest of their lives they are cemented to the ground, using their feathery legs (cirri) to capture plankton.
Once metamorphosis is over and they have reached their adult form, barnacles will continue to grow by adding new material to their heavily calcified plates. These plates are not moulted; however, like all ecdysozoans, the barnacle itself will still molt its cuticle[5].
[edit] Sexual reproduction
Most barnacles are hermaphroditic, although a few species are gonochoric or androdioecious. Typically, recently molted hermaphroditic individuals are receptive as females. Self-fertilization, although theoretically possible, has been experimentally shown to be rare in barnacles [6] [7].
The sessile lifestyle of barnacles makes sexual reproduction difficult, as the organisms cannot leave their shells to mate. To facilitate genetic transfer between isolated individuals, barnacles have extraordinarily long penises, up to 15cm in length: the largest penis to body size ratio of the animal kingdom.[8]
[edit] Fossil record
The geological history of barnacles can be traced back to the early Palaeozoic (in the order of 4-500 million years ago),[1] although they do not become common in the fossil record until the Neogene (last 20 million years). In part their poor preservation is due to their restriction to high-energy environments, which tend to be erosional - therefore it is more common for their shells to be ground up by wave action than for them to reach a depositional setting. It is also possible that the group was more minor in the past.[verification needed]
Barnacles can play an important role in estimating palæo-water depths. The degree of disarticluation of fossils suggests the distance they have been transported, and since many species have narrow ranges of water depths, it can be assumed that the animals lived in shallow water and broke up as they were washed down-slope. The completeness of fossils, and nature of damage, can thus be used to constrain the tectonic history of regions.[2]
[edit] In human culture
Barnacles were first fully studied and classified by Charles Darwin who published a series of monographs in 1851 and 1854. Darwin undertook this study at the suggestion of his friend Joseph Dalton Hooker, in order to thoroughly understand at least one species before making the generalisations needed for his theory of evolution by natural selection [9].
Barnacles are of economic consequence as they 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.[citation needed]
Some barnacles are edible by humans, and goose barnacles (e.g. Pollicipes polymerus) are treasured as a delicacy in many Mediterranean countries.[citation needed] The resemblance of this barnacle's fleshy stalk to a goose's neck gave rise in ancient times to the notion that geese, or at least certain seagoing species of wild goose, literally grew from the barnacle.[citation needed] Most notably, the wild Barnacle Goose (Branta leucopsis), whose eggs and young were rarely seen by humans because it breeds in the remote Arctic, got its popular name because it was imagined to grow from gooseneck barnacles.[citation needed]
[edit] Classification
Some authorities regard Cirripedia as a full class or subclass, and the orders listed above are sometimes treated as superorders. This article follows Martin and Davis in placing Cirripedia as an infraclass of Thecostraca and in the following classification of cirripedes down to the level of orders [10][opinion needs balancing]:
Infraclass Cirripedia Burmeister, 1834
[edit] External links
Wikimedia Commons has media related to:
- Rock barnacle at Aquascope
- Barnacles from the Marine Education Society of Australasia
- Barnacles in Spain Article on barnacles in Spain, and their collection and gastronomy.
- [1] Newcastle University's barnacle and biofouling information site.
[edit] References
Balanidae, Mission Beach National Park, Queensland, Australia, 2002
- , a b Foster, B.A. & Buckeridge, J.S. 1987: Barnacle palaeontology. In Southward, A.J. (ed.): Barnacle Biology, 41-63. Balkema, Rotterdam.
- , a b c d e f g h i j k l Doyle, P.; Mather, A.E.; Bennett, M.R.; Bussell, A. (1997). "Miocene barnacle assemblages from southern Spain and their palaeoenvironmental significance". Lethaia 29: 267-274. doi:10.1111/j.1502-3931.1996.tb01659.x.
- , Zimmer, Carl (2000), Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures, Free Press.
- , Stanley, S.M. (2008). "Predation defeats competition on the seafloor". Paleobiology 34 (1): 1-21. Retrieved on 2008-05-13.
- , Bourget, E. 1987 Barnacle shells: Composition, structure, and growth. In: Crustacean Issues 5: Barnacle Biology (A.J. Southward, ed). pp. 267-285. ISBN 90-6191-628-3
- , Barnacle general biology. Museum Victoria (1996).
- , Charnov, E.L. 1987. Sexuality and hermaphroditism in barnacles: A natural selection approach. In: Crustacean Issues 5: Barnacle Biology (A.J. Southward, ed). pp. 89-103. ISBN 90-6191-628-3
- , http://www.museum.vic.gov.au/crust/barnbiol.html
- , Étienne Benson. Charles Darwin. SparkNotes. Retrieved on 2007-08-30.
- , Joel W. Martin & George E. Davis (2001). An Updated Classification of the Recent Crustacea. Natural History Museum of Los Angeles County.
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