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Crab. The popular name for a considerable group of invertebrate animals belonging to the class Crustacea, of which there are numerous species, exceedingly various in size, color, and modes of living. Like other crustaceans, their bodies are covered by an external skeleton or calcareous crust; they have ten jointed limbs, adapted for walking; the breathing is performed by means of gills. The head and the breast are united, constituting the cephalothorax, and the whole covered by a strong carapace. Tm tail, or abdomen, is very short, and is tucked up beneath the cephalothorax out of view; it is employed by the females to carry eggs. In the main features of their anatomy the crabs do not differ essentially from the lobster and the crawfish. The sense of sight is peculiarly acute, and enables them to distinguish the approach of objects at a considerable distance. The mouth is furnished with strong jaws, in addition to which the stomach has its internal surface studded with hard projections, or teeth, for the purpose of grinding the food. The liver is of great size, and constitutes that soft, rich, yellow substance, found immediately beneath the shell, and called the fat of the crab. The crabs, like the lobsters, molt, or throw off their entire calcareous covering, periodically, when they are soft and helpless, and usually conceal themselves until a new crust is formed. Most of them are littoral in their habits, dwelling upon the shores of the sea or those of creeks and rivers, but some live inland, and are known as land crabs.

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