CRAB, a name common to all the species of short-tailed Decapod Crustaceans ( Brachyura), as well as to the forms intermediate between the short-tailed and long-tailed groups (Anomourd), and derived from the Latin Carabus, the name by which the common edible species was known to the Romans. The abdomen in the true crabs is short, and is completely folded beneath the breast. In the female this part is broad and rounded, and bears certain leafy appendages to which the ova are attached before spawning; in the male the abdomen is much narrower and is somewhat triangular in shape. Like all other Decapod Crustaceans crabs are furnished with ten legs, of which the anterior pair are modified so as to form nippers—powerful prehensile organs and principal weapons of offence. These are largest in the male, and the right claw is generally larger than the left. The other limbs usually end in a single claw, which in the posterior pair in swimming-crabs is more or less flattened and paddle-like ( Plate X. fig. 2). Their eyes, which are compound, are placed upon stalks, measuring in some instances an inch in length (Plate X. fig. 3), and these when not in use fit into cavities in the carapace or shell which covers the entire upper surface. Crabs, like insects, undergo metamorphosis. On emerging from the egg they are provided with long tails, swimming appendages, and sessile eyes, and bear so little resemblance to the parent form that until half a century ago their connection with the crab was altogether unsuspected. They were then known as zoeas. After moulting, the eyes appear on stalks and nippers on the anterior pair of legs, but this form is still sufficiently uncrablike to have deceived early zoologists, who described it as forming a distinct genus (Megalops), and it is not till ...a further casting of the skin that the creature assumes the perfect form. As its internal parts continue to grow its external shell soon becomes too small, and is cast off,—the crab generally concealing itself until its new and greatly enlarged covering gets sufficiently hardened. This process of moulting takes place very frequently in the young crab, and gradually becomes rarer as the creature approaches its full growth, crabs being often found with oysters attached to the carapace which from their size must have grown there for three or four years. A still more remarkable power is that possessed by crabs of reproducing limbs which have been voluntarily thrown off, or have been lost by accident. This renewal only takes place when the limb has been severed at the second articulation; but when broken at any point nearer the extremity the creature generally succeeds in throwing off the part between.
Among the numerous species of crabs which abound everywhere on or near the sea-coast tho following may be noticed.
(1) The Great or Edible Crab (Cancer pagurus), the Carabus of the Romans and the Partan of Scotland. This is one of the largest, and as an article of food is certainly the most valuable, of the short-tailed Decapods, being everywhere esteemed for the delicacy of its flavour. It abounds chiefly on the rocky parts of the coasts of Europe, and often measures 12 inches across the carapace, weighing in the larger specimens fully 12 lb. The principal British crab-fisheries are off the north-east coast of Scotland, in the Firth of Forth, and off the coast of Cornwall; and the home produce is largely supplemented by imports from Norway. In the capture of this crustacean “crab-pots,” made of wicker-work, with the entrance at the top, and baited with dead fish, are employed. These are sunk in the proper localities, and their position indicated by a piece of cork attached to a line connected with the wicker trap. In the sheltered bays of the west of Scotland this crab is also caught in calm weather by poking it from behind with a long pole, which the crustacean immediately seizes, and which is then gently shaken, making the crab adhere all the more tenaciously, and giving the fisherman the opportunity he seeks of hoisting it into his boat. When caught, crabs are kept alive till wanted by being placed in perforated boxes which are then sunk at some convenient spot in the sea. Those caught off Lizard Point are conveyed to Falmouth Harbour, where they are individually branded, and put in boxes which are then placed under water. Recently it was stated on good authority, that one of those cases having gone to pieces, thus liberating the imprisoned crabs, many of them were shortly after caught again on their old feeding-ground—a distance of eleven miles from the place where they had been confined. As they had been conveyed to Falmouth by boat, it is impossible with our present knowledge to say by what sense they were thus unerringly guided on their return journey.
(2) The Shore Crab (Carcinus maenas) is the species most commonly met with on all parts of the British coast. Although found in deep water, its favourite haunts are beneath the stones that lie between low and high water mark, and its awkward sidelong gait as it sidles off to its place of concealment must be familiar to the most casual observer of shore life. It is a shy creature, eluding observation beneath stones or buried in the sand, its telescopic eyes alone visible, and feigning death when unable otherwise to cope with danger. Unlike the former species, its legs, especially the posterior pair, are flattened and ciliated so as to form swimming organs. Owing probably to the small size of this species, it has obtained little prominence as an article of food, although in flavour it is said to rival the Great Crab. Large numbers, however, are eaten by the poorer classes in seaport towns, and they are also to be had in the London fish markets. They feed chiefly on the spawn of fish and the smaller crustaceans.
(3) Pea Crabs (Pinnotheres, Plate X. fig. 5) are small crustaceans ii which the sexes so differ that the males and females were at one time described as separate species. The female is larger than the male, and its external covering is softer; and they are further remarkable in taking up their residence in the shells of living bivalve mollusks, especially in the pinna, the cockle, and the mussel. The soft-bodied female is never found outside of its adopted shell, although the harder cased male is thus occasionally met with. The Pinna Pea Crab (Pinnotheres veterum), which abounds in the Mediterranean, makes its home in the pinna shell, and ancient writers have given highly imaginative descriptions of the object of this alliance between crustacean and mollusk. It was believed that on the entrance of food “within the gaping circuit of the shell,” the active little crab pricked the tender sides of its sluggish partner, who understanding the hint closed its shell upon the prey
“Thus fed by mutual aid, the friendly pair Divide their gains, and all the plunder share.”
(4) The Inachus Kempferi, found in Japanese waters, is the largest of known crabs. It measures 10 feet between the tips of its nippers, each of which is 5 feet in length. The body, however, is comparatively small and triangular in shape. It is said to be eaten by the Japanese.
(5) Land Crabs occur in various parts of the tropical world, and are especially abundant in the West Indies. The Violet Land Crab (Gecarcinus ruricola, Plate X. fig. 1) of Jamaica lives in communities and forms burrows in the ground, often two or three miles from the sea. These crabs are provided with powerful pincers, which they are not loath both to use and to lose, for when attacked they fix upon the enemy with their great claw, which is then thrown off, and as the muscles connected with it retain their tension for some time after the severance, the creature seeks to make its escape while pain is still being inflicted by the now independent claw. They remain in their burrows by day, and come forth at night in search of food, running about with great speed and retiring, when possible, to their holes, in the presence of danger. They renew their connection with the sea once a year, visiting it in order to deposit their spawn. They travel by night, directed by a powerful instinct which causes them to march straight for their destination, surmounting whatever difficulties may be in their way. At this season they are taken in great numbers, and their flesh is regarded as one of the chief delicacies of the island. Like their marine congeners they cast their shell, but unlike these, it is immediately after the moulting process that they are in best condition for the table. The Calling Crab (Gelasimus tetragonon) of Ceylon has its left claw exceedingly small, while its fellow is larger than all the rest of the body, and this it carries aloft as if brandishing a weapon (see Crustacea, fig. 65); while the Racer Crab (Ocypoda ceratoph-thalma) digs deep burrows in the sandy roads of that island, sufficient to render them dangerous for horsemen, were the holes not regularly filled up by a band of labourers.
(6) The Robber Crab (Birgus latro) belongs to that division (Anomoura) of the Decapod Crustaceans which forms a connecting link between crabs and lobsters, the abdominal segments not being folded beneath the breast as in true crabs. It is an inhabitant of the islands in the Indian Ocean, and makes its burrows under the cocoa-nut trees, the fruit of which forms its principal food. It was formerly supposed to ascend these trees and break off tho nuts, but the researches of Darwin, Bennet, and others seem to prove that they only make use of the nuts which they find already fallen. In order to get at the edible contents of these, they strip off the fibrous envelope so as to lay bare the eye-spots, into one of which they insert the sharp edge of a claw, and by working this backward and forward they gradually scoop out the substance of the nut. According to another authority, after inserting the claw, they sometimes proceed to crack the hard shell by beating it against a stone. The fibre which they remove from the nut is employed by them in lining their burrows; it is also gathered by the natives and made into mats, &c. The Robber Crab attains a length of 2 feet, and has usually a mass of fat under the tail which, according to Darwin, often yields when melted as much as a quart of limpid oil.
(7) In the Hermit Crabs (Paguridae, Plate X. fig. 7) the abdomen is soft and pulpy and destitute of protecting plates, the safety of this defenceless part being provided for by the entrance of those creatures into univalve shells to which they become so closely attached by means of certain hooked appendages of the abdomen, that it is impossible to drag a Hermit Crab from its adopted shell without tearing the body asunder. The mouth of the shell is guarded by the claw, the larger pincers of some of these crabs being, says Darwin, “most beautifully adapted when drawn back to form an operculum to the shell nearly as perfect as the proper one.” The most common and the largest of the British species is the Soldier Crab (Pagurus bernhardus, Plate X. fig. 4), to be seen at all seasons on our coasts, inhabiting a great variety of univalve shells from the tiny natica to the largest whelk, the latter being the shell usually chosen by the adult crab. It changes its residence so soon as it has outgrown the dimensions of the place, and its new premises seem to be generally selected with a view to the future growth of the creature. Dead shells appear in some cases to .be thus employed, but it is believed that in most instances the crab kills the mollusk in order to secure its shell. Hermit Crabs are largely used as bait. See Crustacea.