|
|
| (20 intermediate revisions by 15 users not shown) |
| Line 1: |
Line 1: |
| − | {{otheruses}}
| + | [[Image:SallyLightfootCrab.jpg|right|thumb|300px|Sally Lightfoot crab]] |
| − | {{Taxobox
| + | '''Crabs''' are a large family of [[decapod]] [[crustacean]]s. There are hundreds of [[species]], mainly [[marine]], although [[freshwater]] species such as the [[Chinese]] [[mitten crab]], and land-dwelling species such as the [[robber crab]] (which climbs [[coconut]] trees to feed on the [[nut]]s), also exist. |
| − | | color = pink
| |
| − | | name = Crabs
| |
| − | | image = Blue crab on market in Piraeus - Callinectes sapidus Rathbun 20020819-317.jpg
| |
| − | | image_width = 250px | |
| − | | image_caption = ''[[Blue crab|Callinectes sapidus]]'' | |
| − | | regnum = [[Animal]]ia | |
| − | | phylum = [[Arthropod]]a
| |
| − | | subphylum = [[Crustacean|Crustacea]]
| |
| − | | classis = [[Malacostraca]]
| |
| − | | ordo = [[Decapoda]]
| |
| − | | subordo = [[Pleocyemata]]
| |
| − | | infraordo = '''Brachyura'''
| |
| − | | infraordo_authority = [[Pierre André Latreille|Latreille]], 1802
| |
| − | | subdivision_ranks = Superfamilies
| |
| − | | subdivision =
| |
| − | *[[Dromiacea]]
| |
| − | **[[Homolodromidae|Homolodromioidea]]
| |
| − | **[[Dromioidea]]
| |
| − | **[[Homoloidea]]
| |
| − | *[[Eubrachyura]]
| |
| − | **[[Raninoidea]]
| |
| − | **[[Cyclodorippoidea]]
| |
| − | **[[Dorippoidea]]
| |
| − | **[[Calappoidea]]
| |
| − | **[[Leucosioidea]]
| |
| − | **[[Majoidea]]
| |
| − | **[[Hymenosomatidae|Hymenosomatoidea]]
| |
| − | **[[Parthenopoidea]]
| |
| − | **[[Retroplumidae|Retroplumoidea]]
| |
| − | **[[Cancroidea]]
| |
| − | **[[Portunoidea]]
| |
| − | **[[Bythograeidae|Bythograeoidea]]
| |
| − | **[[Xanthoidea]]
| |
| − | **[[Belliidae|Bellioidea]]
| |
| − | **[[Potamoidea]]
| |
| − | **[[Psuedothelphusidae|Pseudothelphusoidea]]
| |
| − | **[[Gecarcinucoidea]]
| |
| − | **[[Cryptochiridae|Cryptochiroidea]]
| |
| − | **[[Pinnotheridae|Pinnotheroidea]] *
| |
| − | **[[Ocypodoidea]] *
| |
| − | **[[Grapsoidea]] *
| |
| − | <small>An asterisk (*) marks the crabs included in the clade [[Thoracotremata]].</small>
| |
| − | }}
| |
| − | '''Crabs''' are [[Decapoda|decapod]] [[crustacean]]s of the infraorder '''Brachyura''', which typically have a very short "tail" ([[Greek language|Greek]]: ''brachy'' = short, ''ura'' = tail), or where the abdomen is entirely hidden under the thorax. They are generally covered with a thick [[exoskeleton]], and are armed with a single pair of [[chela]]e ([[claw]]s). Crabs are found in all of the world's oceans; there are also many [[fresh water|freshwater]] and [[terrestrial animal|terrestrial]] crabs, particularly in tropical regions. Crabs vary in size from the [[pea crab]], only a few [[millimetre]]s wide, to the [[Japanese spider crab]], with a leg span of up to 4 [[metre|m]] <ref>{{cite web |url=http://oceanlink.island.net/records.html |title=Biggest, Smallest, Fastest, Deepest: Marine Animal Records |publisher=OceanLink |accessmonthday=September 22 |accessyear=2006}}</ref>. | |
| | | | |
| − | ==Anatomy==
| + | The [[Alaska]]n [[king crab]] is the heaviest species of crab, but the [[Japan]]ese [[spider crab]] has much longer legs, sometimes spanning ten feet or more.<ref>http://www.vincelewis.net/spider.html</ref> The smallest species of crabs are the [[pea crab]]s, that live as [[commensal]]s inside the shells of many [[bivalve]] [[mollusc]]s. |
| − | True crabs have five pairs of [[arthropod leg|legs]], the first of which is modified into a pair of claws and is not used for locomotion. In all but a few crabs (for example, [[Raninoida]]), the [[abdomen]] is folded under the [[cephalothorax]]. The [[mouthparts]] of crabs are covered by flattened [[maxilliped]]s, and the front of the [[carapace]] does not form a long [[Rostrum (anatomy)|rostrum]] <ref>{{cite journal | quotes=no|author = Dixon, C. J., [[Frederick Schram|F. R. Schram]] & S. T. Ahyong|year=2004|title=A new hypothesis of decapod phylogeny|journal=[[Crustaceana]]|volume=76|issue=8|pages=935–975}}</ref>. The [[gill]]s of crabs are formed of flattened plates ("phyllobranchiate"), resembling those of [[shrimp]], but of a different structure <ref>{{cite journal | quotes=no |author=Taylor, H. H. & E. W. Taylor |year=1992 |title=Gills and Lungs: The Exchange of Gases and Ions |journal=Microscopic Anatomy of Invertebrates |volume=10 |pages=203–293}}</ref>.
| |
| | | | |
| − | Most crabs show clear [[sexual dimorphism]] and so can be easily sexed. The abdomen, which is held recurved under the thorax, is narrow in males. In females, however, the abdomen retains a greater number of [[pleopod]]s and is considerably wider <ref>{{cite web |url=http://www.dnr.sc.gov/marine/sertc/Glossary.pdf |publisher=Southeastern Regional Taxonomic Center |title=Glossary of terms for decapods |format=[[Portable Document Format|PDF]]}}</ref>. This relates to the carrying of the [[fertilisation|fertilised]] eggs by the female crabs (as seen in all [[Pleocyemata|pleocyemates]]). In those species in which no such dimorphism is found, the position of the gonopores must be used instead. In females, these are on the third [[pereiopod]], or nearby on the sternum in higher crabs; in males, the gonopores are at the base of the fifth pereiopods or, in higher crabs, on the sternum nearby.
| + | Crabs are typically [[omnivorous]], feeding primarily on [[algae]], but happy to scavenge or capture live prey when available. Crabs are themselves the common prey of many marine [[organism]]s, including [[cod]], [[cuttlefish]] and [[octopus]]es. |
| | | | |
| − | ==Diet==
| + | Crabs are an important fishery in many parts of the world. |
| − | Crabs are [[omnivore]]s, feeding primarily on [[alga]]e <ref>{{cite journal |quotes=no |title=Natural diet of the crab ''Notomithrax ursus'' (Brachyura, Majidae) at Oaro, South Island, New Zealand |author=Woods, C. M. C. |journal=[[New Zealand Journal of Marine and Freshwater Research]] |year=1993 |Volume=27 |pages=309=315 |url=http://www.rsnz.org/publish/nzjmfr/1993/29.php}}</ref>, and taking any other food, including [[mollusc]]s, [[worm]]s, other [[crustacean]]s, [[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 (biology)|fitness]] <ref>{{cite journal |quotes=no |title=Diet composition influeces the fitness of the herbivorous crab ''Grapsus albolineatus'' |journal=[[Oecologia]] |author=Kennish, R. |volum=105 |issue=1 |year=1996 |pages=22-29 |url=http://www.springerlink.com/content/l7m3368427059312/}}</ref><ref>{{cite journal |quotes=no |title=Diet choice in an omnivorous salt-marsh crab: different food types, body size, and habitat complexity |author=Buck, T. L., G. A. Breed, S. C. Pennings, M. E. Chase, M. Zimmer & T. H. Carefoot |journal=[[Journal of Experimental Marine Biology and Ecology]] |year=2003 |volume=292 |issue=1 |pages=103-116 |url=http://cat.inist.fr/?aModele=afficheN&cpsidt=14847986}}</ref>. | |
| | | | |
| − | ==Crab fishery==
| + | The [[horseshoe crab]], ''Limulus'', is not actually a crab, or even a crustacean. |
| − | [[Image:Sorting Crabs Ffionphort.jpg|350px|thumb|left|[[Edible crab]]s being sorted by fishermen at [[Fionnphort]], [[Scotland]]]] | + | |
| − | Crabs make up 20% of all marine crustaceans caught and farmed worldwide, with over 1½ million [[tonne]]s being consumed annually. Of that total, one species accounts for one fifth: ''[[Portunus trituberculatus]]''. Other important [[taxon|taxa]] include ''[[Portunus pelagicus]]'', several species in the genus ''[[Chionoecetes]]'', the [[blue crab]] (''Callinectes sapidus''), ''[[Charybdis (genus)|Charybdis spp.]]'', ''[[Edible crab|Cancer pagurus]]'', the [[Dungeness crab]] (''Cancer magister)'' and ''[[Scylla serrata]]'', each of which provides more than 20,000 tonnes annually <ref>{{cite web |url=http://www.fao.org/figis/servlet/TabLandArea?tb_ds=Capture&tb_mode=TABLE&tb_act=SELECT&tb_grp=COUNTRY |title=Global Capture Production 1950-2004 |publisher=[[Food and Agriculture Organization|FAO]] |accessmonthday=August 26 |accessyear=2006}}</ref>.
| + | Crabs were known to the Ancient Greeks, as evidenced by the existence of a crab [[constellation]], Cancer, which is also one of the twelve signs of the [[zodiac]]. |
| − | <br clear="left">
| |
| − | ==Evolution and classification==
| |
| − | The infraorder Brachyura contains about 70 [[family (biology)|families]], as many as the remainder of the [[Decapoda]] <ref name="Martin & Davis">{{cite book |url=http://www.nhm.org/research/publications/CrustaceaClassification.pdf |title=An Updated Classification of the Recent Crustacea |author=Martin, J. W. & G. E. Davis |year=2001 |pages=132 pp. |publisher=Natural History Museum of Los Angeles County |format=[[Portable Document Format|PDF]]}}</ref>. The evolution of crabs is characterised by an increasing robustness of the body, and a reduction in the abdomen. Although other groups have also undergone similar processes of [[carcinisation]], it is most advanced in crabs. The [[telson]] is no longer functional in crabs, and the [[uropod]]s are absent, having probably evolved into small devices for holding the reduced abdomen tight against the sternum <ref>{{cite journal | quotes=no |author=Guinot, D & J.–M. Bouchard |year=1998 |title=Evolution of the abdominal holding systems of brachyuran crabs (Crustacea, Decapoda, Brachyura) |journal=[[Zoosystema]] |volume=20 |issue=4 |pages=613–694 |url=http://www.mnhn.fr/publication/zoosyst/z98n4a4.html |format=[[Portable Document Format|PDF]]}}</ref>.
| |
| − | | |
| − | In most decapods, the [[gonopore]]s (sexual openings) are found on the legs. However, since crabs use the first two pairs of [[pleopod]]s (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 (arthropod)|sternum]] <ref>{{cite journal | quotes=no |author=De Saint Laurent, M. |year=1980 |title=Sur la classification et la phylogénie des Crustacés Décapodes Brachyoures. II. Heterotremata et Thoracotremata Guinto, 1977 |journal=[[C. R. Acad. Sc. Paris]] |volume=t. 290 |pages=1317–1320}}</ref>. 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 [[Monophyly|monophyletic group]] <ref name="Martin & Davis"/>.
| |
| − | | |
| − | The earliest unambiguous crab [[fossil]]s date from the [[Jurassic]], although the [[Carboniferous]] ''Imocaris'', known only from its [[carapace]] is thought to be a primitive crab <ref>{{cite journal | quotes=no |author=[[Frederick Schram|Schram, F. R.]] & R. Mapes |year=1984 |title=''Imocaris tuberculata'', n. gen., n. sp. (Crustacea: Decapoda) fro the upper Mississippian Imo Formation, Arkansas |journal=[[Transactions of the San Diego Society of Natural History]] |volume=20 |issue=11 |pages=165–168}}</ref>. The [[Adaptive radiation|radiation]] of crabs in the [[Cretaceous]] and afterwards may be linked either to the break-up of [[Gondwana]] or to the concurrent radiation of [[Osteichthyes|bony fish]], the main [[predator]]s of crabs <ref>{{cite journal | quotes=no |author=Wägele, J. W. |year=1989 |title=On the influence of fishes on the evolution of benthic crustaceans |journal=J. zool. Syst. Evolut.-forsch. |volume=27 |pages=297–309}}</ref>.
| |
| − | | |
| − | About 850 species <ref>{{cite journal | quotes=no |author=Sternberg, R. von & N. Cumberlidge |year=2001 |title=On the heterotreme-thoracotreme distinction in the Eubrachyura De Saint Laurent, 1980 (Decapoda: Brachyura) |journal=[[Crustaceana]] |volume=74 |pages=321–338}}</ref> of crab are freshwater or (semi-)terrestrial species; they are found throughout the world's [[tropic]]al and [[Subtropics|semi-tropical]] regions. They were previously thought to be a closely related group, but are now believed to represent at least two distinct [[Lineage (evolution)|lineages]], one in the [[Old World]] and one in the [[New World]] <ref>{{cite journal | quotes=no |author=Sternberg, R. von, N. Cumberlidge & G. Rodriguez |year=1999 |title=On the marine sister groups of the freshwater crabs (Crustacea: Decapoda: Brachyura) |journal=[[J. Zool. Syst. Evol. Research]] |volume=37 |pages=19–38}}</ref>.
| |
| − | | |
| − | ==Gallery==
| |
| − | <gallery>
| |
| − | Image:Corystes cassivelaunus.jpg|[[Masked crab]], ''Corystes cassivelaunus''
| |
| − | Image:Liocarcinus vernalis.jpg|''[[Liocarcinus vernalis]]''
| |
| − | Image:Atelecyclus rotundatus museum.jpg|[[Circular crab]], ''Atelecyclus rotundatus''
| |
| − | Image:Gecarcinus ruricola.jpg|The terrestrial [[halloween crab]], ''Geocarcinus ruricola''
| |
| − | Image:Stenorhynchus seticornis 2.jpg|[[Arrow crab]] ''Stenorhynchus seticornis''
| |
| − | Image:Grapsus grapsus.JPG|"Sally lightfoot", ''[[Grapsus grapsus]]''
| |
| − | Image:Thia scutellata.jpg|[[Thumbnail crab]], ''Thia scutellata''
| |
| − | Image:Spider crabs at the Kaiyukan Aquarium in Osaka close.jpg|[[Japanese spider crab]], ''Macrocheira kaempferi''
| |
| − | Image:Ocypode quadrata (2).jpg|[[Ghost crab]], ''Ocypode quadrata''
| |
| − | Image:Fiddler crab.jpg|[[Fiddler crab]], ''Uca pugnax''
| |
| − | Image:Lyreidus tridentatus.jpg|''Lyreidus tridentatus'', a [[Raninidae|raninid]]
| |
| − | Image:Hepatus epheliticus.jpg|''Hepatus epheliticus'', a calico crab
| |
| − | </gallery>
| |
| − | | |
| − | ==Similar animals==
| |
| − | Several other groups of animals are either called crabs or have the term "crab" in their names. These include [[hermit crab]]s, [[porcelain crab]]s and [[king crab]]s, which, despite superficial similarities to true crabs, belong to the [[Anomura]]. The [[United Kingdom|UK]] [[Food Standards Agency]] allows [[king crab]]s to be sold as "crab" <ref>{{cite web |url=http://www.food.gov.uk/multimedia/webpage/namesoffish |title=UK list of legal names for fish species |publisher=[[Food Standards Agency]] |date=[[2003-09-26]]}}</ref>, but this practice is not followed outside the [[food industry]]. Others, such as [[horseshoe crab]]s are much more distantly related. Anomuran "crabs" can be distinguished from true crabs by counting the legs. In Anomura, the last pair of [[pereiopod]]s (walking legs) is hidden inside the [[carapace]], so only four pairs are visible (counting the claws), whereas uninjured true crabs generally have five visible pairs (in the family Hexapodidae, the last pair of pereiopods is [[Vestigial structure|vestigial]] <ref>{{cite journal |quotes=no |title=Rediscovery of the holotype of ''Paeduma cylindraceum'' (Bell, 1859) and description of a new genus of Hexapodidae (Decapoda, Brachyura) |author=Guinot, D. |journal=[[Zoosystema]] |volume=28 |issue=2 |pages=553–571 |year=2006 |url=http://www.mnhn.fr/museum/front/medias/publication/8150_z06n2a26.pdf |format=[[Portable Document Format|PDF]]}}</ref>).
| |
| | | | |
| | ==References== | | ==References== |
| − | {{commonscat|Brachyura}}
| + | <references/> |
| − | {{Wikispecies|Brachyura}}
| |
| − | <div class="references-small"><references/></div> | |
| | | | |
| − | [[Category:Crabs| ]] | + | [[Category:Crustaceans]] |
| − | [[Category:Edible crustaceans]] | + | [[Category:Seafood]] |
| | + | [[Category:Non-Kosher Animals]] |
