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crab, crustacean with an enlarged cephalothorax covered by a broad, flat shell called the carapace. Extending from the cephalothorax are the various appendages: five pairs of legs, the first pair bearing claws (or pincers), are attached at the sides; two eyes on short, movable stalks, two short antennules, two longer antennae, and numerous mouthparts are attached at the front; at the rear the tiny abdomen is bent under the cephalothorax.
The abdomen of the female, wider and flatter than that of the male, forms an apronlike structure that continuously circulates water over the eggs that are carried on her underside. The free-swimming larva, which hatches in about two weeks, is easily recognized by the large spine that projects from its carapace. After several molts, the young crab settles to the bottom and begins to take on adult features.
Crabs are chiefly marine, but some are terrestrial for long periods. They are omnivorous; some are scavengers and others predators. Although they are capable of locomotion in all directions, crabs tend to move sideways; swimming crabs have the last pair of legs flattened to form paddles.
The blue crab of the Atlantic coast of the United States is a swimming crab that is much used for food. It is marketed as a soft-shelled crab after it has molted and before the new shell has hardened. Females of the oyster and mussel crabs live inside the shells of bivalve mollusks. Often seen scurrying about near their burrows in muddy banks are the fiddler crabs, the males of which have one much enlarged claw used in defense and in courtship rituals. The sand, or ghost, crabs build burrows high up on the sand into which they seem to vanish. The sluggish, long-legged spider crabs are often disguised by the algae, barnacles, and sea anemones that attach themselves to the carapace. The giant spider crab of Japan, the largest living arthropod, has legs about 4 ft (22 cm) long and a carapace over 1 ft (30 cm) wide. The closely related kelp crabs are found in kelp beds in the Pacific. The name king crab is applied to the largest (up to 20 lb/9 kg) of the edible crabs, species native to the N Pacific and marketed frozen, canned, or fresh; the red king crab has been introduced into the Barents Sea.
True crabs are classified in the phylum Arthropoda, subphylum Crustacea, order Decapoda. Although the many species of true crabs are similar in appearance, DNA evidence suggests that that similarity is a result of convergent evolution among several groups of sometines only distantly related decapods. The horseshoe crab, which also is called by the name king crab, is not a crustacean, and the hermit crab, although a crustacean, is not a true crab.
See J. S. Weis, Walking Sideways: The Remarkable World of Crabs (2012).
Crab(religion, spiritualism, and occult)
Crab is a popular name for the sign Cancer. Its association with moody Cancer is the ultimate source of the term “crabby.”
What does it mean when you dream about a crab?
A symbol of both the sea and the sky, the crab can stand for physical nourishment from the ocean and intellectual nourishment from the interpretation of the horoscope. Claws are tenacious and clinging, which can indicate something about the relationships the dreamer is in, especially with the opposite sex.
ii. To fly with wings level but apply significant rudder to offset the effects of crosswind.
iii. In parachuting, it means facing one's chute on a diagonal to the wind or crosswind, similar to tacking in a sailboat.
iv. To fly with wings level but with significant yaw due to asymmetric power or thrust.
v. In aerial photography, the angle formed between the flight line and the edges of the photographs in the direction of flight. At the instant of exposure, if the focal plane of the camera is not square with the direction of flight, it causes crab of the photograph. In this process, there is some reduction of overlap as shown in the illustration.
vi. The rotation of an aircraft about its vertical axis, so as to cause the aircraft's longitudinal axis to deviate from the flight line.