AskDefine | Define crabs

Dictionary Definition

crabs n : infestation of the pubic hair by crab lice [syn: pediculosis pubis]

User Contributed Dictionary

English

Pronunciation

  • /kræbz/
    Rhymes with: -æbz

Noun

crabs
  1. Plural of crab
  2. pubic lice

Translations

slang: pubic lice

Verb

crabs
  1. third-person singular of crab

Extensive Definition

Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (Greek: brachy = short, ura = tail), or where the reduced abdomen is entirely hidden under the thorax. They are generally covered with a thick exoskeleton, and are armed with a single pair of chelae (claws). About 6000 species are known. Crabs are found in all of the world's oceans. Additionally, there are also many freshwater and terrestrial crabs, particularly in tropical regions. Crabs vary in size from the pea crab, only a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 m.

Diet

Crabs are 8 legged omnivores, some feeding primarily on algae, others taking any type of food, including mollusks, 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.

Crab fishery

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

Evolution and classification

The infraorder Brachyura contains about 93 families, as many as the remainder of the Decapoda. 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 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. 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. The radiation of crabs in the Cretaceous and afterwards may be linked either to the break-up of Gondwana or to the concurrent radiation of bony fish, the main predators of crabs.
About 850 species 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 closely related group, but are now believed to represent at least two distinct lineages, one in the Old World and one in the New World.

Gallery

Cultural influences of the crab

The Moche people of ancient Peru worshipped nature, especially the sea. They placed emphasis on animals and often depicted crabs in their art.

References

See also

crabs in Old English (ca. 450-1100): Crabba (dēor)
crabs in Min Nan: Hē
crabs in Catalan: Cranc
crabs in Czech: Krab
crabs in Danish: Krabbe
crabs in German: Krabben
crabs in Estonian: Krabilised
crabs in Spanish: Brachyura
crabs in Esperanto: Krabo
crabs in French: Brachyura
crabs in Croatian: Rakovi
crabs in Scottish Gaelic: Partan
crabs in Indonesian: Kepiting
crabs in Italian: Brachyura
crabs in Latin: Cancer
crabs in Lithuanian: Krabas
crabs in Malagasy: Foza
crabs in Malay (macrolanguage): Ketam
crabs in Dutch: Krabben
crabs in Korean: 게
crabs in Japanese: カニ
crabs in Norwegian: Krabber
crabs in Polish: Krab
crabs in Portuguese: Caranguejo
crabs in Romanian: Crab
crabs in Russian: Краб
crabs in Finnish: Taskuravut
crabs in Swedish: Krabbor
crabs in Tamil: நண்டு
crabs in Thai: ปู
crabs in Turkish: Yengeç
crabs in Vietnamese: Cua
crabs in Ukrainian: Краби
crabs in Chinese: 螃蟹
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