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SHARK
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SHARK , a Selachian See also:fish (see See also:SELACHIANS), belonging to the See also:order Plagiostomi, suborder Squali. Sharks are almost exclusively inhabitants of the See also:sea, but some See also:species enter the mouths of large See also:rivers, and one species (Carcharias gangeticus) occurs frequently high up in the large rivers of See also:India. C. nicaraguensis of the See also:lake of See also:Nicaragua and the Rio See also:San Juan appears to have taken up its See also:residence permanently in fresh See also:water. Sharks are most numerous between the tropics, a few only reaching the See also:Arctic circle; it is not known how far they advance S. in the See also:Antarctic region. Altogether some See also:hundred and fifty different species have been described. With regard to their habits many are littoral species, the See also:majority pelagic, and a few are known to belong to the deep-sea See also:fauna, having hitherto been obtained down to a See also:depth of nearly 1000 fathoms. Littoral Sharks.—The littoral forms are of small See also:size, and generally known under the name of " See also:dog-fishes," " hounds," &c. Some pelagic sharks of larger size also live near the See also:shore on certain parts of. a See also:coast, but they are attracted to it by the abundance of See also:food, and are as frequently found in the open sea, which is their birthplace; therefore we shall refer to them when we speak of the pelagic kinds. The majority of the littoral species live on the bottom, some-times See also:close inshore, and feed on small marine animals or on any See also:animal substance. The following are deserving of See also:special See also:notice. The tope (Galeus) is See also:common on the coasts not only of See also:England, See also:Ireland and of S. See also:Europe, but also of S. See also:Africa, See also:California, See also:Tasmania and New See also:Zealand. Its See also:teeth are
equal in both jaws, of rather small size, See also:flat, a triangular, with the point directed towards the one See also:side, and with a notch and denticulations on the shorter side (fig. 1). It is of a See also:uniform slaty-See also:grey See also:colour, and attains to a length of 6 ft. The See also:female brings forth some See also:thirty living See also:young at one See also:birth in May. It becomes trouble-some at times to fishermen by taking their bait and See also:driving away other fish they See also:desire
to catch. The fins of G. zyopterus of the Californian coast are much esteemed for culinary purposes by the See also:Chinese.
The hounds proper (Mustelus) possess a very different dentition, the, teeth being small, obtuse, numerous, arranged in several rows like See also:pavement (fig. 2). Five or six species are known from the shores of the various temperate and subtropical seas, one (M. vulgaris) being common on the coasts of See also:Great See also:Britain and the See also:United States, on the Pacific as
well as the See also:Atlantic side. It is of a uniform grey colour or sparingly spotted with See also: It is comparatively harmless and feeds on shells, crustaceans and decomposing animal substances.
The dogfishes proper (Scyllium, Chiloscyllium, &c.) are spread
over nearly all the temperate and tropical seas. Their teeth are
small, in several See also:series, with a longer pointed See also:cusp in the See also:middle,
and generally one or two smaller ones on each side (See also:figs. 3 and 5).
They are all oviparous, their oblong See also:egg-shells being produced
at each corner into a See also:long See also:thread by which the egg is fastened to
some fixed See also:object. Some of the
tropical species are ornamented
with a See also:pretty See also:pattern of colora-
tion. The two See also:British species,the
lesser and the larger spotted dog-
fish (Sc. canicula and Sc. See also:catulus),
belong to the most common fishes
of the coast and are often See also:con-
founded with each other. But the
former is finely dotted with See also: The ground colour is a brownish-yellow, ornamented with black or brown transverse bands or rounded spots. It is a littoral species, but adult specimens, which are from To to 15 ft. long, are met far from See also:land. It is easily recognized by its enormously long bladelike tail, which is See also:half as long as the whole fish. The teeth are small, trilobed, in many series. The See also:fourth and fifth gill-openings are close together. The genus Crossorhinus, of which three species are known from the coasts of See also:Australia and Japan, is remarkable as the only instance in this See also:group of fishes in which the integuments give a " celative " rather than a " protective " resemblance to their surroundings. Buccal Cavities of the same fish. of the mouth, or See also:form a See also:wreath See also:round the side of the See also:head, and the irregular and varied coloration of the whole See also:body closely assimilates that of a See also:rock covered with See also:short See also:vegetable and coralline growth. The species of Crossorhinus grow to a length of io ft. The so-called See also:Port See also:Jackson shark (Heterodontus=Cestracion) is likewise a littoral form. Besides the common species (H. See also:philippi), three other closely allied kinds from the Indo-Pacific are known. This genus, which is the only existing type of a See also:separate See also:family, is one of special See also:interest, as similar forms occur in See also:Primary and Secondary strata. The jaws are armed withsmall obtuse teeth in front, which in young individuals are pointed, and provided with from three to five cusps. The lateral teeth are larger, See also:pad-like, twice as broad as long and arranged in oblique series (fig. 7). The fossil forms far exceeded in size the living, which scarcely attain to a length of 5 ft. The shells of their eggs are found thrown ashore like those of our dogfishes. The See also:shell is pyriform, with two broad lamellar ridges each See also:wound edgewise five times round it (fig. 8).
The spiny or piked dogfish (Acanthias) inhabits the temperate seas of both the N. and S. hemispheres. For some See also:part of the See also:year it lives in deeper water than the sharks already noticed,
but at uncertain irregular times it appears at the See also:surface and close inshore in almost incredible numbers. See also:Couch says that he has heard of 20,000 having been taken in a See also:seine at one See also:time; and in See also: 9). The spiny
dogfish are of a greyish colour, with some whitish spots in young specimens, and attain to a length of 2 or 3 ft. They are viviparous, the young being produced throughout the summer months.
Finally, we have to notice among the littoral sharks the " See also:angel-fish " or " See also: b Of the more remarkable forms which we Acanthias vulgaris. See also:dandy represented in species and individuals is Carcharias, now split up by 'many authors into several separate genera. Perhaps nine-tenths of the sharks of which we read in books of travel belong to this genus. Between thirty and See also:forty species have been distinguished, all of which are found in tropical seas. They are the sharks which so readily attach themselves to sailing vessels, following them for See also:weeks. Others affect more the neighbourhood of land. One of. the most common species is the See also:blue shark (Carcharias See also:glaucus), of which specimens (4 to 6 ft. long) are frequently caught on the S. coasts of England and Ireland. Other species of Carcharias attain a length of 3o ft. The mouth of all is armed with a series of large flat triangular teeth, which have a See also:sharp, smooth or serrated edge (fig. to). Galeocerdo is likewise a large shark very dangerous to man, differing from the preceding chiefly by having the See also:outer side of its teeth deeply notched. It has long been known to occur in the N. Atlantic, close to the Arctic Ocean (G. arcticus), but its existence in other parts has been ascertained within a See also:recent See also:period; in fact, it seems to be one of the most common and dangerous sharks of the Indo-Pacific, the British Museum having obtained specimens from See also:Mauritius, Kurrachee, See also:Madras and the W. coast of Australia. Hammerheaded sharks (Sphyrna= Zygaena) are sharks in which the anterior FIG. 11.-Upper and portion of the head is produced into a See also:Lower Tooth of Lamna. See also:lobe on each side, the extremity of which is occupied by the eye. The relation of this unique configuration of the head to the See also:economy of the fish is unknown. Otherwise these sharks resemble Carcharias, and are equally formidable, but seem to be more stationary in their habits. They occur in all tropical and subtropical seas, even in the Mediterranean, where S. Zygaena is by no means rare. In the Indian Ocean it is common, and Cantor states that specimens may be often seen ascending from the clear blue depths of the ocean like a great See also:cloud. The porbeagles (Lamm) differ from the preceding sharks in their dentition and are not dangerous to man; at least there is na instance known of a See also:person having been attacked by the species common on the British coast (L. cornubica). This is referred to in the See also:works of older British authors as " See also:Beaumaris shark." The short and stout form of its body contrasts strikingly with its much attenuated tail, which, however, is strengthened by a See also:keel on each side and terminates in a large and powerful caudal fin. The snout is pointed, and the jaws are armed with strong lanceolate teeth, each of which bears a small cusp on each side of the See also:base (see fig. rr). The teeth are not adapted for cutting, like the flat triangular teeth of man-eating sharks, but rather for seizing and holding the See also:prey, which consists chiefly of various kinds of fishes and cephalopods. In the upper See also:jaw there are from thirteen to sixteen teeth on each side, the third being remarkable for its small size; in the lower jaw from twelve to fourteen. The gill-openings are very wide. The porbeagle attains to a length of ro or rz ft., ails is a pelagic fish, not rare in the N. Atlantic and Mediterranean, and frequently wandering to the British and more rarely to the See also:American shores. This species is widely distributed over the N. of the Atlantic and Pacific Oceans. Other closely allied species (L. spallanzanii, L. glauca) are known to occur in the S. Atlantic, from the Mediterranean to the. Cape of See also:Good See also:Hope. To the genus Carcharodon particular interest is attached, because the single still existing species is the most formidable of all sharks, as were those which preceded it in See also:Tertiary times. The existing species (C, rondeletii) occurs in almost all tropical and subtropical seas, but seems to be verging towards extinction. It is known to attain to a length of 40 ft. The tooth figured U II., See also:section; rondeletii. here of the natural size (fig. 12) is taken from a jaw much shrunk in drying, but still 20 in. wide in its transverse See also:diameter, and taken from a specimen 362 ft. long. The See also:extinct species must have been still more gigantic in bulk, probably reaching a length of qo ft., as we may See also:judge from teeth which are found in the See also:crag or which were dredged up from the Pacific Ocean by the " Challenger " expedition, and which are 4 in. wide at the lase and 5 in. long measured along their lateral margin. In some Tertiary strata these teeth are extremely abundant, so much so that—for instance, in See also:Florida—the strata in which they occur are quarried to obtain the fossil remains for export ro England, where they are converted into artificial manure. The See also:fox-shark or thresher (Alopecias vulpes), of which every year specimens are captured on the British coast, but which is common in the N. and S. hemispheres, is readily recognized by its extremely slender tail, the length of which exceeds that of the See also:remainder of the body. Its teeth are small, flat, triangular and without serrature. It follows the shoals of See also:herrings, pilchards and sprats in their migrations, destroying incredible numbers and frequently injuring the nets. When feeding it uses the long tail in splashing the surface of the water, whilst it swims in gradually decreasing circles round a shoal of fishes which are thus kept crowded together. Sometimes two threshers may be seen working together. Statements that it has been seen to attack whales and other large cetaceans See also:rest upon erroneous observations; its dentition is much too weak to bite through their skin. The thresher attains to a length of 15 ft., the tail included. The basking shark (Selache See also:maxima), sometimes erroneously called " See also:sunfish," is the largest fish of the N. Atlantic, growing to a length of more than 30 ft. Though best known from the N. of the Atlantic or Pacific oceans, this species has also been recorded from the Australian seas. The mouth is of an extra-See also:ordinary width, and, like the gill-cavity, capable of great expansibn, so as to enable the fish to take at one gulp an enormous quantity of the small fish and other marine creatures on which it subsists. Also the gill-clefts are of great width, and the See also:internal opening of each is guarded by a See also:kind of strainer, formed by the enormously_ elongated gill-rakers, which serves to prevent the food organisms from passing out through the clefts. The teeth are very small, numerous, arranged in several series, conical and probably without use in feeding. This shark is therefore quite harmless if not attacked. Off the W. coast of Ireland it was at one time hunted for the See also:sake of the oil from the See also:liver, one fish yielding from a ton to a ton and a half. Its See also:capture is not unattended with danger, as one See also:blow from the tail is sufficient to,stave in the sides of a large See also:boat. The basking shark is gregarious, and may be seen in See also:calm See also:weather lying with the upper part of the back raised above the surface of the water, a See also:habit which it has in common with the true sunfish (Orthagoriscus), and from which it has derived its name. A shark similar in many points to the basking shark, and an inhabitant of the Indo-Pacific Ocean, is Rhinodon typicus. So far as our See also:present knowledge goes, it is the largest of all sharks, as it is known to•exceed a length of 5D ft., but it is stated to attain that of qo. The captures of only a few specimens are on See also:record, at the Cape of Good Hope and near the See also:Seychelles, where it is known as the " chagrin." The snout is extremely short, broad and flat, with the mouth and nostrils placed at its extremity; the gill-openings very wide, and the eye very small. The teeth are extremely small and numerous, conical in shape. No opportunity should be lost of obtaining exact See also:information on this shark. The same applies to the allied Micristodus punctatus recorded from off the W. coast of See also:America. The See also:Greenland shark (Laemargus borealis) belongs to the same family as the spiked dogfish, but grows to a much larger size, specimens 26 ft. long having been met with. The two dorsal fins are small and destitute of spines. The teeth (fig. 15) in the upper jaw are small, narrow, conical in shape; those of the lower flat, arranged in several series, one on the See also:top of the other, so that only the uppermost forms the sharp dental edge of the jaw. The points of these lower teeth are so much turned aside that the inner margin only enters the dental edge. The Greenland shark is an inhabitant of the Arctic regions, sometimes straying to the latitudes of Great Britain and of Cape See also:Cod in the W. Atlantic; it is one of the greatest enemies of the See also:whale, which is often found with large pieces bitten out of the tail by this shark. Its voracity is so great that, as See also:Scoresby tells us, whilst engaged in feeding on the carcase of a whale it will allow itself to be stabbed with a See also:lance or See also:knife without being driven away. The spinous shark (Echinorhinus spinosus) is readily recognized by the short bulky form of its body, its short tail, and the large round bony tubercles which are scattered all over its body, each of which is raised in the middle into a pointed conical spine. While most frequently recorded from the E. Atlantic, specimens have also been obtained from the coasts of N. America and of New Zealand. It always lives on the bottom, and probably descends to some depth. It does not seem to exceed a length of ro ft. Bathybial Sharks.—Sharks do not appear to have yet reached the greatest depths of the ocean; and so far as we know at present we have to See also:fix the limit of their See also:vertical See also:distribution at See also:I000 fathoms. Those which we find to have reached or to pass the roo fathoms See also:line belong to generic types which, if they include littoral species, are ground-sharks—as we generally find the bottom-feeders of our littoral fauna much more strongly represented in the deep sea than the surface swimmers. All belong to two families only, the Scylliidae and Spinacidae, the littoral members of which live for the greater part habitually on the bottom and probably frequently reach to the too fathoms line. Distinctly bathy- bial species are two small dogfishes— Spinax granulatus from 120 fathoms, and Scyllium canescens from 400 fathoms, both on the S.W. coast of S. America; also Cent- roseyllium granulatum from 340 fathoms in the S. Ocean, whose congener from the coast of Greenland probably descends to a similar depth. The shark which reaches the greatest depth recorded hitherto appears to be Scyllio- rhinus indicus obtained by the See also:Valdivia ex- pedition from a depth of nearly I000 fathoms in the W. Indian Ocean. It belongs to the genus Centrophorus, of which some ten species are known, all from deep water in the N. Atlantic, Mediter- ranean, the Molucca and See also:Japanese seas. The Japanese species were discovered by the naturalists of the " Challenger " on the Hyalonema ground off. Inosima in 345 fathoms. Dr E. P. See also:Wright found C. coelolepis at a still greater depth on the coast of See also:Portugal. The fishermen of See also:Setubal fish for these sharks in 400 or 500 fathoms, with a line of some 600 fathoms in length. " The sharks caught were from 3 to 4 ft. long, and when they were hauled into the boat See also:fell down into it like so many dead pigs "; in fact, on being rapidly withdrawn from the great pressure under which they lived they were killed, like other deep-sea fishes in similar circumstances. It is See also:note-worthy that the organization of none of these deep-sea sharks has undergone such a modification as would See also:lead us to infer that they are inhabitants of great depths. One of the most, interesting types of the See also:division of sharks is the small family of Notidanidae, which is externally distinguished by the presence of a single dorsal fin only, without spine and opposite to the anal, and by having six or seven wide branchial openings. They represent an See also:ancient type, the presence of which in See also:Jurassic formations is shown by teeth extremely similar to those of the living species. Their See also:skeleton is notochordal. Only four species are known, of which one (Notidanus griseus) has now and then strayed N. to the See also:English coast. Allied tothe Notidanidae are the Chlamydoselachidae or frilled sharks, represented so far as is known by a single living species, C. anguineus Garman (fig. 16), which occurs frequently in deep water off the coast of Japan and as isolated specimens off the coasts of New See also:South See also:Wales, See also:Madeira and See also:Norway. A fossil species has been described from the See also:Pliocene of N. See also:Italy. It resembles a conger in shape, and differs from the Notidani proper by its elongated body, wide nearly terminal mouth, extremely wide gill-openings and peculiarly formed teeth. The teeth are similar in both jaws, each composed of three slender curved cusps separated by a pair of See also:minute intermediate points, and with a broad base directed backwards. A few words may be added with reference to the economic uses of this group of fishes. As mentioned above some of the smaller dog-fishes are eaten at certain seasons by the captors, and by the poorer classes of the See also:population. An inferior kind of oil, chiefly used for the See also:adulteration of cod-liver oil, is extracted on some of the N. fishing-stations from the liver of the spiked dogfishes, and occasionally of the larger sharks. See also:Cabinet-makers make extensive use of shark's. skin under the name of "See also:shagreen " for smoothing or polishing See also:wood. This shagreen is obtained from species (such as our dog-fishes) whose skin is covered with small, pointed, closely-set, calcified papillae, whilst very rough skins, in which the papillae are large or See also:blunt, are useless for this purpose. The dried fins of sharks (and of rays) form in India and China an important See also:article of See also:trade, the Chinese preparing See also:gelatin from them, and using the better sort for culinary purposes. They are assorted in two kinds, viz. " white " and " black." The former consists exclusively of the dorsal fins, which are reputed to yield more gelatin than the other fins. The pectoral, ventral and anal fins constitute the black " sort; the caudal are not used. (A. C. G.; J. G. Additional information and CommentsThere are no comments yet for this article.
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