Page:The New International Encyclopædia 1st ed. v. 05.djvu/615

CRAB. 529 CBAB. CRAB (AS. l-rabba, Icel. krabbi, Ger. Erabbe). A crustacean of the onlcr Decapoda and suborder Brachyura, characterized by the small size of the abdomen, which resemliles a 'short tail curved under the thorax, all important viscera being included in the thorax. The term extends also to some of the suborder Anonuira (purse-crabs, hermit-crabs, etc.), characterized by a condition of abdomen intermediate between that of the Brachjiira and that of the Macrnra, or long-tailed decapod crustaceans, such as the lobster, crayfish, etc. All the crabs, besides many other crustaceans, were comprehended in the Linna-an genus Cancer; but the num- ber of species is ver3' great, consideral)ly more than 1000, and the Brachyura alone are now arranged in many genera and families. The^e 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 lieak, etc. ; also in its smoothness, or roughness with hairs, tubercles, or spines ; in the length of the' legs, etc. The eyes are compound, with hexag- onal facets, and are elevated on stalks, which are generally short, but sometimes considerably lengthened, and which have the power of mo- tion, so as to turn the eye in different directions. The first pair of limbs are not used for locomo- tion, but e.hibit in great perfection the char- acteristic claws or pincers {chrlar) of the deca- pod crustaceans. Crabs are inhabitant's of al- most all seas; most of them, however, are found chiefly 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 thus expanded, and some- times occur far out at sea. LARVAL STAGES OF CRABS. a, zoea stage ; b. megalops stage. Their development is accomplished by metamor- 7)hosis through succeeding stages. "In the crabs the nauplius stage (see CRrsT.CE.) is passed through in the egg. and the young is hatched in the form of a peculiarly modified zoea, with an injmense cephalothorax produced into spines, large stalked eyes, and a slender abdomen. This passes by successive molts into the meqalops stage, which resembles an adult macruran [and] . . . passes by successive molts into the adult form." Cralis, like all arthropods (see Arthropoda), molt or change their shell, not at fixed intervals or seasons, but according to the exigencies of their growth, Uie change being made with great fre- quency when they are very young, but rarely in advanced age; indeed, from the niollusks and other animals sometimes foiuid adhering to the carapace, it is inferred tluit 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 pugnacdty. The luimber of specimens is apt, howc^ver, 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 nundier of species and their wide distribution. The giant crab of .fapan (Macrochira Kcemp(cri) , 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 are usually larger, and their abdomens broader and more oval, while males have the ehelip more powerfully developed^nota- bly so in the fiddlers. Economic Importance of Crabs. — These animals supplj' 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 (Caliinectes hnstatns) , hundreds of thou- sands 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 Commens.^lism) are regarded as a great luxuiw. In Europe the species most fre- quently used are those of the genus Cancer, especially the great Cancer pagiirus, and there is no reason why the two eastern American sjie- cies of this genus, the 'rock' and '.Tonah' crabs (qq.v. ), should not be far mor" utilized as food than Wiey are. To this group belong the prin- cipal edible crab of the American Pacific coast {Cancer mac/ister), and others smaller which are eaten by the Chinese, etc. This s])ccies 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. ^lany are taken in wicker traps or 'pots.' baited with meat or offal ; another common method is to sink shal- low hoop-nets of coarse material and mesh, which are bailed and hauled up rapidly at intervals, bringing the crabs with them. Hand-line fishing, with b idles 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 f!ulf of Mexico trawls or 'trot-lines' are set in several ways, and vast quantities of crabs arc thus taken. They are kept for market in floating pens or