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Dictionary Definition

crab

Noun

1 decapod having eyes on short stalks and a broad flattened carapace with a small abdomen folded under the thorax and pincers

2 a quarrelsome grouch [syn: crabby person]

3 (astrology) a person who is born while the sun is in Cancer [syn: Cancer]

4 the fourth sign of the zodiac; the sun is in this sign from about June 21 to July 22 [syn: Cancer, Cancer the Crab]

5 the edible flesh of any of various crabs [syn: crabmeat]

6 infests the pubic region of the human body [syn: crab louse, pubic louse, Phthirius pubis]

7 a stroke of the oar that either misses the water or digs too deeply; "he caught a crab and lost the race"

Verb

1 direct (an aircraft) into a crosswind

2 scurry sideways like a crab

3 fish for crab

4 complain; "What was he hollering about?" [syn: gripe, grouse, beef, squawk, bellyache, holler] [also: crabbing, crabbed]

User Contributed Dictionary

English

Pronunciation

, /kræb, /kr

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

Synonyms, Antonyms and Related Words

Chinese windlass, Dungeness crab, Japanese crab, Spanish windlass, air a grievance, bank, beef, bellyache, bellyacher, bitch, bleat, blue point, bollix, capstan, cat flea, chigoe, clam, clamor, cockroach, complain, complainant, complainer, coquillage, cramp, crane, crank, crawdad, crawfish, crayfish, crib, crimp, croak, croaker, crosspatch, derrick, dip, dog flea, erector, faultfinder, feather, fishtail, flea, forklift, foul up, fret, fret and fume, frondeur, fuss, gantry crane, grayback, gripe, griper, groan, grouch, grouse, grouser, growl, growler, grumble, grumbler, grunt, gum, gum up, hoist, holler, howl, hydraulic tailgate, jack, jackscrew, jigger, kick, kicker, kvetch, langouste, lever, lift, lifter, limpet, littleneck clam, lobster, lodge a complaint, loop, louse, louse up, malcontent, mite, murmur, murmurer, mussel, mutter, mutterer, nit, oyster, parasite, periwinkle, plow, porpoise, prawn, pull out, pull up, push down, quahog, queer, querulous person, raise a howl, reactionary, reactionist, rebel, red bug, reel, register a complaint, roach, roll, sand flea, scallop, shellfish, shrimp, sideslip, skid, snafu, snail, soft-shell crab, sorehead, spin, spiral, squawk, steamer, stunt, tackle, take on, undulate, vermin, weevil, whelk, whiner, winch, windlass, yammer, yap, yaw, yawp, yelp

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