CRAB

CRАВ (AS. krabba, Icel. krabbi, Ger. Krabbe). A crustacean of the order Decapoda and suborder Brachyura, characterized by the small size of the abdomen, which resembles a short tail curved under the thorax, all important viscera being included in the thorax. The term extends also to some of the suborder Anomura (purse-crabs, hermit-crabs, etc.), characterized by a condition of abdomen intermediate between that of the Brachyura and that of the Macrura, or long-tailed decapod crustaceans, such as the lobster, crayfish, etc. All the crabs, besides many other crustaceans, were comprehended in the Linmvan genus Cancer; but the number of species is very great, considerably more than 1000, and the Brachyura alone are now arranged in many genera and families.
 

1. FIDDLER CRAB (Qelaslmus pugnax).
2. HERMIT CRAB I Eupagurus longlcarpus)
3. HERMIT, out of Its borrowed shell, showing reduced and defenseless posterior parts.
4. EASTERN EDIBLE O" BLUE CRAB iCallinectes hastatus).
5. A DEEP-SEA CRAB (North Atlantic) Its arms closed Into Natica héros. a defensive box.
6. COCOANUT CRAB (Blrgus latro).
7. COMMON CRAB OF PACIFIC COAST (Cancer maglster).
8. SPIDER CRAB (Liblnla emarglnata).

These various crabs differ very much in the form of the carapace (the back), which in some is orbicular or nearly so; in some, much broader than it is long; in others, longer than broad; in some, prolonged in front into a kind of beak, etc. ; also in its smoothness, or roughness with hairs, tubercles, or spines; in the length of the legs. etc. The eyes are compound, with hexagonal facets, and are elevated on stalks, which are generally short, but sometimes considerably lengthened, and which have the power of motion, so as to turn the eye in different directions. The first pair of limbs are not vised for locomotion, but exhibit in great perfection the characteristic claws or pincers (chclœ) of the decapod crustaceans. Crabs are inhabitants of almost all seas; most of them, however, are found C'hielly near the coast. Some crabs inhabit fresh water, particularly in the warmer parts of the world; and others, known as land-crabs, live among moist herbage, or burrow in sand or earth. Crabs are generally flesh or carrion eaters, though some forms seem to prefer a vegetarian's diet. They are always active and are noted for running sideways, rather than straight ahead. Some have the last pair of limbs expanded at the extremity into a broad blade for swimming, and some have even all the four pairs of limbs intended for locomotion Unis expanded, and sometimes occur far out at sea.

Crabs, like all arthropods (see Arthropoda), molt or change their shell, not at fixed intervals or seasons, but according to the exigencies of their growth, the change being made with great frequency when they are very young, but rarely in advanced age; indeed, from the mollusks and other animals sometimes found adhering to the carapace, it is inferred that the same covering is sometimes worn for a number of years.

Crabs become interesting in the aquarium, from their readiness in seizing food, their activity in tearing and eating it, and their pugnacity. The number of specimens is apt, however, to be soon diminished by the stronger killing and eating the weaker. Crabs vary greatly in size and color, as might be expected from the great number of species and their wide distribution. The giant crab of Japan (ifacroctiira Kœmpfcri), although only a foot across the disk, which is 18 inches long, has such long legs as occasionally to be 15 to 18 feet from tip to tip of the first pair. The great stone-crab of Tasmania, which has short and very thick legs, has been known to reach a weight of over 30 pounds. On the other hand, many species of crab are only a fraction of an inch across. In color, crabs vary from black to white, through all the colors of the rainbow. Shades of green, blue, and gray are perhaps the most common, but the brightest shades of red and yellow are by no means rare. The sexes of crabs are easily distinguished, as the females arc usually larger, and their abdomens broader anil more oval, while males have the chehe more powerfully developed—notably so in the fiddlers.

Economic Importance of Crabs.—These animals supply food for food-fishes, are of great service as scavengers, and are used as human food in various parts of the world. In the United States the principal crab so used is the blue crab (Callincctcs hautains), hundreds of thousands of which are sent to market every year from the waters of Chesapeake Bay alone. The little pea-crabs (Pinnotheres) often found in oysters (see COMMEN8ALISM) are regarded as a great luxury. In К u ropo the species most frequently used are those of the genus Cancer, especially the great Cancer panurus, and there is no reason why the two eastern American species of this genus, the 'rock' and 'lonah' crabs (qq.v.l. should not he far more utilized as food than they are. To this group belong the principal edible crab of the American Pacific coast (Cancer maaistcr), and others smaller which are eaten by the Chinese, etc. This species usually measures 7 to 9 inches in breadth of body, and abounds from Alaska to Mexico, usually below low-tide level on sandy bottom. Crabs which have just shed their shell, and are covered only by a soft skin, are regarded as best, and are called 'shedders* or 'soft-shelled.'

The ways of fishing are various. Many are taken in wicker traps or 'pots.' baited with ment or offal ; another common method is to sink shallow hoop-nets of coarse material and mesh, which «re baited and hauled up rapidly at intervals, bringing the crabs with them. Hand-line fishing, with bundles of meat to which the crabs cling until lifted out of water, is more a sport than a method of market-fishing; but in the Gulf of Mexico trawls or 'trot-lines' are set in several ways, and vast quantities of crabs are thus taken. They are kept for market in floating pens or 'cars,' and shipped alive packed in wet seaweed. They are also preserved by canning, etc.  -- The New international encyclopaedia, Volume 5 edited by Daniel Coit Gilman, Harry Thurston Peck, Frank Moore Colby: 1920 and Stanley L. Klos 1999


 

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