Kepiting beraneka ragam ukurannya, dari [[ketam kacang]], yang lebarnya hanya beberapa [[milimeter]], hingga [[kepiting laba-laba Jepang]], dengan rentangan kaki hingga 4 [[meter|m]] <ref>{{cite web |url=http://oceanlink.island.net/records.html |title=Biggest, Smallest, Fastest, Deepest: Marine Animal Records |publisher=OceanLink |accessdaymonth=22 September |accessyear=2006}}</ref>.
kepiting adalah hewn aneh masa ada cangkang nya
== Anatomi ==
Kepiting sejati mempunyai lima pasang [[kaki artropoda|kaki]]; sepasang kaki yang pertama dimodifikasi menjadi sepasang capit dan tidak digunakan untuk bergerak. Di hampir semua jenis kepiting, kecuali beberapa saja (misalnya, [[Raninoida]]), perutnya terlipat di bawah [[cephalothorax]]. Bagian [[mulut]] kepiting ditutupi oleh [[maxilliped]] yang rata, dan bagian depan dari [[carapace]] tidak membentuk sebuah [[Rostrum (anatomi)|rostrum]] yang panjang <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>. [[Insang]] kepiting terbentuk dari pelat-pelat yang pipih ("phyllobranchiate"), mirip dengan insang [[udang]], namun dengan struktur yang berbeda <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.
==Diet==
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==
[[Berkas: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]] |accessdaymonth=August 26 |accessyear=2006}}</ref>.
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==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>.
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== Galeri ==
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