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Crabs
Fossil range: Jurassic–Recent
Liocarcinus vernalis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Brachyura
Linnaeus, 1758
Sections & subsections [1]

True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (Greek: βραχύ/brachy = short, ουρά/οura = tail), or where the reduced abdomen is entirely hidden under the thorax. Other animals, such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs and crab lice, are not true crabs.

Contents

Evolution

Crabs are generally covered with a thick exoskeleton, and armed with a single pair of chelae (claws). Crabs are found in all of the world's oceans, while many crabs live in freshwater and on land, particularly in tropical regions. Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 metres (13 ft) [2].

About 850 species [3] of crab are freshwater or (semi-)terrestrial species; they are found throughout the world's tropical and semi-tropical regions. They were previously thought to be a monophyletic group, but are now believed to represent at least two distinct lineages, one in the Old World and one in the New World [4].

The earliest unambiguous crab fossils date from the Jurassic, although Carboniferous Imocaris, known only from its carapace, may be a primitive crab [5]. The radiation of crabs in the Cretaceous and afterward may be linked either to the break-up of Gondwana or to the concurrent radiation of bony fish, crabs' main predators [6].

Sexual dimorphism

The underside of a male (top) and a female (bottom) individual of Pachygrapsus marmoratus, showing the difference in shape of the abdomen

Crabs often show marked sexual dimorphism. Males often have larger claws [7], a tendency which is particularly pronounced in the fiddler crabs of the genus Uca (Ocypodidae). In fiddler crabs, males have one claw which is greatly enlarged and which is used for communication, particularly for attracting a mate [8]. Another conspicuous difference is the form of the pleon (abdomen); in most male crabs, this is narrow and triangular in form, while females have a broader, rounded abdomen [9]. This is due to the fact that female crabs brood fertilised eggs on their pleopods.

Behaviour

Carpilius convexus consuming Heterocentrotus trigonarius in Hawaii

Crabs typically walk sideways [10] (a behaviour which gives us the word crabwise). This is because of the articulation of the legs which makes a sidelong gait more efficient [11]. However, some crabs prefer to walk forwards or backwards, including raninids [12], Libinia emarginata [13] and Mictyris platycheles [10]. Some crabs, notably the Portunidae and Matutidae, are also capable of swimming [14].

Crabs are mostly active animals with complex behaviour patterns. They can communicate by drumming or waving their pincers. Crabs tend to be aggressive towards one another and males often fight to gain access to females [15]. On rocky seashores, where nearly all caves and crevices are occupied, crabs may also fight over hiding holes [16].

Crabs are omnivores, feeding primarily on algae [17], and taking any other food, including molluscs, worms, other crustaceans, fungi, bacteria and detritus, depending on their availability and the crab species. For many crabs, a mixed diet of plant and animal matter results in the fastest growth and greatest fitness [18][19].

Crabs are known to work together to provide food and protection for their family, and during mating season to find a comfortable spot for the female to release her eggs [20].

Human consumption

Fisheries

Photo of crabs in large, open metal box surrounded by fishermen
Fishermen sorting edible crabs at Fionnphort, Scotland

Crabs make up 20% of all marine crustaceans caught, farmed, and consumed worldwide, amounting to 1½ million tonnes annually. One species accounts for one fifth of that total: Portunus trituberculatus. Other commercially important taxa include Portunus pelagicus, several species in the genus Chionoecetes, the blue crab (Callinectes sapidus), Charybdis spp., Cancer pagurus, the Dungeness crab (Metacarcinus magister) and Scylla serrata, each of which yields more than 20,000 tonnes annually [21].

Cookery

Photo of cooked crab in bowl of soup
Crab masala from Karnataka, India

Crabs are prepared and eaten as a dish in several different ways all over the world. Some species are eaten whole, including the shell, such as soft-shell crab; with other species just the claws and/or legs are eaten. The latter is particularly common for larger crabs, such as the snow crab.

In some regions spices improve the culinary experience. In Asia, masala crab and chilli crab are examples of heavily spiced dishes. In Maryland, blue crab is often eaten with Old Bay Seasoning.

For the British dish Cromer crab, the crab meat is extracted and placed inside the hard shell. One American way to prepare crab meat is by extracting it and adding a flour mix, creating a crab cake.

Crabs are also used in bisque, a global dish of French origin.

Pain

Live crabs are often boiled. In 2005, Norwegian scientists concluded that lobsters cannot feel pain [22]. However, later research suggests that crustaceans are indeed able to feel and remember pain [23].

Classification

The infraorder Brachyura contains 6,793 species in 93 families [14], as many as the remainder of the Decapoda [24]. The evolution of crabs is characterised by an increasingly robust body, and a reduction in the abdomen. Although many other groups have undergone similar processes, carcinisation is most advanced in crabs. The telson is no longer functional in crabs, and the uropods are absent, having probably evolved into small devices for holding the reduced abdomen tight against the sternum.

In most decapods, the gonopores (sexual openings) are found on the legs. However, since crabs use the first two pairs of pleopods (abdominal appendages) for sperm transfer, this arrangement has changed. As the male abdomen evolved into a narrower shape, the gonopores have moved towards the midline, away from the legs, and onto the sternum [25]. A similar change occurred, independently, with the female gonopores. The movement of the female gonopore to the sternum defines the clade Eubrachyura, and the later change in the position of the male gonopore defines the Thoracotremata. It is still a subject of debate whether those crabs where the female, but not male, gonopores are situated on the sternum, form a monophyletic group [24].

Superfamilies

Numbers of extant and extinct (†) species are given in brackets [14].

Cultural influences

Both the constellation Cancer and the astrological sign Cancer are named after the crab, and depicted as a crab. John Bevis first observed the Crab Nebula and its resemblance to the animal in 1731. The Crab pulsar lies at the centre of the nebula.

The Moche people of ancient Peru worshipped nature, especially the sea [26]. They often depicted crabs in their art [27].

Western cultures have been influenced by the crab towards the game crab soccer, where players rest and move on an inverted all-fours pose.

References

  1. ^ Sammy De Grave, N. Dean Pentcheff, Shane T. Ahyong et al. (2009). "A classification of living and fossil genera of decapod crustaceans" (PDF). Raffles Bulletin of Zoology Suppl. 21: 1–109. http://rmbr.nus.edu.sg/rbz/biblio/s21/s21rbz1-109.pdf. 
  2. ^ "Japanese spider crab Macrocheira kaempferi". Oceana North America. http://na.oceana.org/en/explore/creatures/japanese-spider-crab. Retrieved January 2, 2009. 
  3. ^ R. von Sternberg & N. Cumberlidge (2001). "On the heterotreme-thoracotreme distinction in the Eubrachyura De Saint Laurent, 1980 (Decapoda: Brachyura)". Crustaceana 74: 321–338. doi:10.1163/156854001300104417. 
  4. ^ R. von Sternberg, N. Cumberlidge & G. Rodriguez (1999). "On the marine sister groups of the freshwater crabs (Crustacea: Decapoda: Brachyura)". Journal of Zoological Systematics and Evolutionary Research 37: 19–38. doi:10.1046/j.1439-0469.1999.95092.x. 
  5. ^ Frederick Schram & Royal Mapes (1984). "Imocaris tuberculata, n. gen., n. sp. (Crustacea: Decapoda) from the upper Mississippian Imo Formation, Arkansas". Transactions of the San Diego Society of Natural History 20 (11): 165–168. 
  6. ^ J. W. Wägele (1989). "On the influence of fishes on the evolution of benthic crustaceans". Zeitschrift für Zoologische Systematik und Evolutionsforschung 27: 297–309. 
  7. ^ L. H. Sweat (August 21, 2009). "Pachygrapsus transversus". Smithsonian Institution. http://www.sms.si.edu/irLspec/Pachyg_transv.htm. Retrieved January 20, 2010. 
  8. ^ M. J. How, J. M. Hemmi, J. Zeil & R. Peters (2008). "Claw waving display changes with receiver distance in fiddler crabs, Uca perplexa". Animal Behaviour 75 (3): 1015–1022. http://richard.eriophora.com.au/pubs/pdf/HowHemmiZeilPeters-07.pdf. 
  9. ^ Guillermo Guerao & Guiomar Rotllant (2009). "Post-larval development and sexual dimorphism of the spider crab Maja brachydactyla (Brachyura: Majidae)". Scientia Marina 73 (4): 797–808. doi:10.3989/scimar.2009.73n4797. http://digital.csic.es/bitstream/10261/19120/3/1148.pdf. 
  10. ^ a b Sally Sleinis & Gerald E. Silvey (1980). "Locomotion in a forward walking crab". Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 136 (4): 301–312. doi:10.1007/BF00657350. 
  11. ^ Andy Horton & Jane Lilley. "Why do crabs walk sideways?". British Marine Life Study Society. http://homepages.ed.ac.uk/evah01/crabs.htm. Retrieved January 5, 2009. 
  12. ^ "Spanner crab Ranina ranina". Fishing and Aquaculture. New South Wales Department of Primary Industries. 2005. http://www.dpi.nsw.gov.au/fisheries/recreational/saltwater/sw-species/spanner-crab. Retrieved January 4, 2009. 
  13. ^ A. G. Vidal-Gadea & J. H. Belanger (2009). "Muscular anatomy of the legs of the forward walking crab, Libinia emarginata (Decapoda, Brachyura, Majoidea)". Arthropod Structure & Development 38 (3): 179–194. doi:10.1016/j.asd.2008.12.002. 
  14. ^ a b c Peter K. L. Ng, Danièle Guinot & Peter J. F. Davie (2008). "Systema Brachyurorum: Part I. An annotated checklist of extant Brachyuran crabs of the world" (PDF). Raffles Bulletin of Zoology 17: 1–286. http://rmbr.nus.edu.sg/rbz/biblio/s17/s17rbz.pdf. 
  15. ^ "Crab (animal)". Encarta. Microsoft. 2005. 
  16. ^ The Miles Kelly Book of Life. Great Bardfield, Essex: Miles Kelly Publishing. 2006. pp. 512. ISBN 978-1842367155. 
  17. ^ C. M. C. Woods (1993). "Natural diet of the crab Notomithrax ursus (Brachyura, Majidae) at Oaro, South Island, New Zealand". New Zealand Journal of Marine and Freshwater Research 27: 309–315. http://www.rsnz.org/publish/nzjmfr/1993/29.php. 
  18. ^ Kennish, R. (1996). "Diet composition influences the fitness of the herbivorous crab Grapsus albolineatus". Oecologia 105 (1): 22–29. doi:10.1007/BF00328787. http://www.springerlink.com/content/l7m3368427059312/. 
  19. ^ T. L. Buck, G. A. Breed, S. C. Pennings, M. E. Chase, M. Zimmer & T. H. Carefoot (2003). "Diet choice in an omnivorous salt-marsh crab: different food types, body size, and habitat complexity". Journal of Experimental Marine Biology and Ecology 292 (1): 103–116. doi:10.1016/S0022-0981(03)00146-1. http://cat.inist.fr/?aModele=afficheN&cpsidt=14847986. 
  20. ^ Danièle Guinot & J.–M. Bouchard (1998). "Evolution of the abdominal holding systems of brachyuran crabs (Crustacea, Decapoda, Brachyura)" (PDF). Zoosystema 20 (4): 613–694. http://www.mnhn.fr/publication/zoosyst/z98n4a4.html. 
  21. ^ "Global Capture Production 1950-2004". FAO. http://www.fao.org/figis/servlet/TabLandArea?tb_ds=Capture&tb_mode=TABLE&tb_act=SELECT&tb_grp=COUNTRY. Retrieved August 26, 2006. 
  22. ^ David Adam (February 8, 2005). "Scientists say lobsters feel no pain". The Guardian. http://www.guardian.co.uk/world/2005/feb/08/research.highereducation. 
  23. ^ "Crabs 'feel and remember pain' suggests new study". CNN. March 27, 2009. http://edition.cnn.com/2009/WORLD/europe/03/27/crabs.memorypain/. 
  24. ^ a b Joel W. Martin & George E. Davis (2001) (PDF). An Updated Classification of the Recent Crustacea. Natural History Museum of Los Angeles County. pp. 132. http://atiniui.nhm.org/pdfs/3839/3839.pdf. 
  25. ^ M. de Saint Laurent (1980). "Sur la classification et la phylogénie des Crustacés Décapodes Brachyoures. II. Heterotremata et Thoracotremata Guinot, 1977". Comptes rendus de l'Académie des sciences t. 290: 1317–1320. 
  26. ^ Elizabeth Benson (1972). The Mochica: A Culture of Peru. New York, NY: Praeger Press. ISBN 9780500720011. 
  27. ^ Katherine Berrin & Larco Museum (1997). The Spirit of Ancient Peru:Treasures from the Museo Arqueológico Rafael Larco Herrera. New York: Thames and Hudson. pp. 216. ISBN 978-0500018026. 

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Wiktionary

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Definition from Wiktionary, a free dictionary

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Contents

English

A crab

Pronunciation

Etymology 1

From Middle English crabbe, from Old English crabba.

Noun

Singular
crab

Plural
crabs

crab (plural crabs)

  1. (zoology) A crustacean of the infraorder Brachyura, having five pairs of legs, the foremost of which are in the form of claws, and a carapace.
  2. A bad-tempered person.
  3. (in plural crabs, informal) An infestation of pubic lice.
    Although crabs themselves are an easily treated inconvenience, the patient and his partner(s) clearly run major STD risks
  4. (slang) A playing card with the rank of three.
Derived terms
Related terms
Translations

Verb

Infinitive
to crab

Third person singular
crabs

Simple past
crabbed

Past participle
crabbed

Present participle
crabbing

to crab (third-person singular simple present crabs, present participle crabbing, simple past and past participle crabbed)

  1. (intransitive) To fish for crabs.
  2. (intransitive) To complain.
  3. (intransitive) (by analogy with the movement of a crab) To move sideways of an aircraft, such as a glider.
  4. (transitive) (by analogy with the movement of a crab) To navigate (an aircraft, e.g. a glider) sideways against an air current in order to maintain a straight-line course.
  5. (obsolete) In World War 1, to fly slightly off the straight-line course towards an enemy aircraft, as the machine guns on early aircraft did not allow firing through the propeller disk.
  6. (rare) To back out of something.
Derived terms

Etymology 2

Germanic: plausibly from Scandinavian, cognate with Swedish dialect scrabba

Noun

Singular
crab

Plural
crabs

crab (plural crabs)

  1. The crab apple or wild apple.
  2. The tree bearing crab apples, which has a dogbane-like bitter bark with medical use.
Synonyms
Derived terms

Verb

Infinitive
to crab

Third person singular
crabs

Simple past
crabbed

Past participle
crabbed

Present participle
crabbing

to crab (third-person singular simple present crabs, present participle crabbing, simple past and past participle crabbed)

  1. (obsolete) To irritate, make surly or sour
  2. To be ill-tempered
  3. (British dialect) To cudgel or beat, as with a crabstick

Etymology 3

EB1911A-pict1.png This entry lacks etymological information. If you are familiar with the origin of this word, please add it to the page as described here.

- possibly a corruption of the Latin genus name Carapa

Noun

Singular
crab

Plural
crabs

crab (plural crabs)

  1. The tree species Carapa guianensis, native of South America.
Derived terms
  • crab-nut
  • crab-oil
  • crab-tree
  • crab-wood

References

  • Weisenberg, Michael (2000) The Official Dictionary of Poker. MGI/Mike Caro University. ISBN 978-1880069523
  • Funk & Wagnalls Standard Dictionary of the English Language. Internatinal Edition. combined with Britannica World Language Dictionary. Chicago-London etc., Encyclopaedia Britannica, inc., 1965.

Anagrams


Simple English

Crabs
Fossil range: Jurassic to Recent
Scientific classification
Kingdom: Animalia
Superphylum: Arthropoda
Phylum: Crustacea
Subphylum: Malacostraca
Class: Decapoda
Order: Brachyura
Linnaeus, 1758

Crabs are in the Phylum Crustacea. They are decapods (ten legs), along with lobsters, crayfish and shrimps. Crabs form an order within the decapods, called the Brachyura. Their short body is covered by a thick exoskeleton.

They are an extremely successful group, found all over the world. They are basically heavily armoured shell-breakers. Most crabs live in sea-water, but there are some who live in fresh water, and some who live on land. The smallest are the size of a pea; the largest (the Japanese Spider Crab) grows to a leg span of 4 metres.[1] About 7,000 species are known.[2]

Contents

Structure and life-style

Body

Crabs have very short tails. A crab's tail and reduced abdomen is entirely hidden under the thorax. It is folded under its body, and may not be visible at all unless you turn the crab over. Usually they have a very hard exoskeleton. This means they are well protected against predators. Crabs are armed with a single pair of claws. Crabs can be found in all the oceans. Some crabs also live in fresh water, or live completely on land.[3]

Pincers

File:Fiddler crab
Anatomy of a fiddler crab

The pincers (claws) of crabs are their most important weapons. They have at least three functions. The pincers' role in eating is to seize and subdue the prey. If the food is a shellfish (mollusc), then the pincers can exert force to open or break the mollusc's shell. Pincers are also used in fighting between males, and for signalling to other crabs.

Food

Crabs are omnivores, they eat almost anything they find. Often this is algae, but animal food is essential for its good health and development. They will eat molluscs, other crustaceans, worms, fungi and bacteria.[4][5]

Crabs as food

Crabs are prepared and eaten all over the world. Some species are eaten whole, including the shell, such as soft-shell crab; with other species just the claws and/or legs are eaten. In some regions spices improve the culinary experience. In Asia, Masala Crab and Chilli crab are examples of heavily spiced dishes. In Maryland, blue crab is often eaten with Old Bay Seasoning.

For the British dish Cromer crab, the meat is extracted and placed inside the hard shell. One American way to prepare crab meat is by extracting it and adding a flour mix, creating a crab cake. Crabs are also used in bisque, a French soup.

Evolution

True crabs appear in the fossil record in the Lower Jurassic. They are part of the 'Mesozoic marine revolution', in which a number of sea-floor predators evolved.[6]

Tailpiece

The closest relatives of the crabs are anomurans, a crustacean group which includes animals such as hermit crabs, king crabs and squat lobsters. They look a lot like crabs and many have the word 'crab' in their name, but are not true crabs. Anomurans can be told apart by the number of legs: crabs have ten legs, including claws, while the last pair of an anomuran's legs is hidden inside the shell, so that only eight legs are visible.

References

  1. "Size of crabs". http://www.buzzle.com/articles/crab-facts.html. 
  2. Walters, Martin & Johnson, Jinny. 2007. The World of Animals. Bath, Somerset: Parragon.
  3. "Where crabs live". http://library.thinkquest.org/CR0215242/crabs.htm. 
  4. Kennish, R. (1996). "Diet composition influeces the fitness of the herbivorous crab Grapsus albolineatus". Oecologia 105 (1): 22–29. doi:10.1007/BF00328787. http://www.springerlink.com/content/l7m3368427059312/. 
  5. Buck T. L. G.A. Breed S.C. Penning M.E. Chase M. Zimmer & T.H. Carefoot (2003). "Diet choice in an omnivorous salt-marsh crab: different food types, body size, and habitat complexity". Journal of Experimental Marine Biology and Ecology 292 (1): 103–116. doi:10.1016/S0022-0981(03)00146-1. http://cat.inist.fr/?aModele=afficheN&cpsidt=14847986. 
  6. Vermeij G.J. 1977. The Mesozoic marine revolution. Evidence from snails, predators and grazers. Paleobiology 3, 135.







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