The Living Animals of the World, Volume II: Birds, Reptiles and Amphibians, Fishes, Jointed Animals, Molluscs, etc.
Photos ly W. Saville-Kenti F.Z.S.] IMilford-on-Sea.
SOUTHERN CROSS PEARL, VALUED AT 10,000. PEARL-SHELL WITH GROUP OP GOLDEN PEARLS.
Consists of nine laterally united pearls corresponding in shape and size. Many thousand shells may be opened without finding a single pearL
Photos by W. Savillc-Kent, F.Z.S.] [Milford-on-Sea.
QUEENSLAND PEARLS ON BLACK-LIPPED PEARL-SHELL. PEARL PRODUCED BY OPERATION ON THE ANIMAL.
The black-lipped shell produces pearls of great value. The pearl produced is a solid hemispherical or " button" pearl. 745
of the World746 The Living Animals
differthe arms, or " cirrhi," of many sea-worms. The superadded valves of the lamp-shells fundamentally from those of the bivalve molluscs in the circumstance that they are developed upon the upper and lower surfaces respectively of the enclosed animal, and not on the sides. The union between the two valves is also accomplished through the medium of interlocking calcareous teeth, in place of a horny or ligamentous hinge-joint, as obtains in an oyster or calcareous support, having a corresponding spiral shape, is alsoa mussel. A supplementary developed in connection with the convoluted arms. This structure varies in the contour of its minuter details in every specific form, which thus furnishes zoologists with a basis for systematic classification. The lamp-shells collectively form two natural groups or orders. In one of these the shells are hinged together, and are of conspicuously unequal dimensions. is more distinctly concave and produced into a perforated beak.The larger shell of the two It is this structure that in some species resembles the wick-hole of an antique lamp, and has given rise to the popular title by which these shells are distinguished. The second or hingeless group is further distinguished by the shells being of almost uniform shape and size. In the most interesting example of this group, known as LINGULA, the two shells are thin, horny, of a green tint, and mounted on a long, flexible, worm-like stalk. Like a worm, this creature moves about in the mud, and constructs a sand-lined dwelling-tube.
Although lamp-shells are represented by comparatively few species at the present day, in the older epochs they existed in enormous abundance. It is further remarkable of this.group that many species are scarcely distinguishable from their fossil ancestors. Lingula, the type last referred to, is especially notable in this respect.
CHAPTER III.
STAR-FISHES, SEA-URCHINS, ETC.
somewhat varied assemblage of marine animals familiarly known as STAR-FISHES,
P"EATHER-STARS, BRITTLE-STARS, SEA-URCHINS, and SEA-CUCUMBERS all agree structurally with one another and differ from all other living organisms in several conspicuous is more orfeatures. Prominent among these is the circumstance that their protecting skin less extensively impregnated externally and strengthened internally with calcareous elements which take the form of plates and spines and spicules. The COMMON SEA-URCHIN may be cited as an example in which these calcareous elements attain their maximum development. The subspherical box-like case or shell, wherein all the vital organs are enclosed and safely protected, is a common object of the seashore, and, empty and denuded of its external coating of prickly spines, familiarly known as a " sea-egg." Examined closely, this shell is found to consist of a series of calcareous plates, which dovetail or fit together in juxtaposition with the utmost nicety. The surface of the shell is studded throughout with rounded hemispherical knobs, those of a larger size having a very distinctly symmetrical plan of distribution. These rounded knobs are the bases of attachment of the spines, which radiate at all points from Photo by W. SavilU-KcnL, F.Z.S.] [Milford on-Sea. the surface of the shell when the animal is COMMON OR SHORT-SPINED SEA-URCHIN. alive. It will be further recognised on a nearer This species is used for food in Italy and other Continental countries. examination that the walls of the shell are pierced
Starfishes, Sea-urchins, etc. 747
on a definitely symmetrical pattern with minute perforations, such perforations being most distinctly visible on the inner surface of the shell. These minute punctures are the apertures through which in life the delicate tubular locomotive organs, or so-called " feet," are thrust out and retracted. The majority of these tubular organs terminate in a circular sucking-disk, wherewith, collectively, the urchin is able to adhere to and travel over the surface of the smoothest rock, or even up the glass walls of an aquarium. In the empty beach-gathered urchin-shell a circular hole may be observed at the two opposite poles, the one in the centre of the lower and natter surface being the larger of the two. It is within this lower and larger one that the mouth, with its complex apparatus of teeth, is suspended.
loto by W. Saville-Kent, F.Z.S.] [Milfonl'on-Sea.
LONG-SPINED SEA-URCHINS.
The nesedle-like spines of these sea-urchins are over a foot in length. Acres of these creatures may be sometimes seen on tidally exposed areas of the Queensland Great Barrier Reef, where this photograph was taken.
The membranous disk which covers the upper and smaller circular, aperture in the living animal is perforated centrally by the vent, and around it are grouped the eye-spots and sundry excretory apertures. A noteworthy feature associated with the greater portion of the structural details of the sea-urchin which have been enumerated is the dominance of the number five in -the constituent elements. It is found, for instance, that the perforated areas through which the tube-feet are protruded form, as with the petals and other elements of many flowers, five symmetrically corresponding segments. The dental apparatus comprises five equivalent tooth-like structures, and there are five eye-spots and five excretory apertures at the upper pole. This particular number, with multiples of the same, is furthermore characteristic of all the typical members
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of the class. Thus, in the COMMON STAR-FISH, there are five so-called arms, five eye-spots, one at the tip of each arm, and five equivalent elemental components of all the more important viscera. In the SEA-CUCUMBERS, which have elongate worm-like bodies, there is a similar apportionment of the nerves and muscles of the body generally into fives, and also of the branching tentacles which surround the mouth. Tubular locomotive organs, " the so-called tube-feet," are common to all the three types enumerated. The calcareous plates and spinules, while attaining to a maximum development in the urchins, are also abundantly represented in the other groups. In
Photo by W. Saville-Kcnt, F.Z.S.'] [Milford-on-Sea. the common star-fish these calcareous THICK-SPINED SEA-URCHIN. elements form within the skin an thick as a slate-pencil, and may be used for the In large specimens the spines are as openly reticulated trellis-like frame- same purpose. work, while in the ordinary sea-cucumbers they more usually take the form of innumerable microscopically minute spicules. The two less familiarly known groups of the FEATHER-STARS and BRITTLE-STARS fully agree with the previously -enumerated types in their five-fold structural composition. The brittle-stars have almost invariably five arms only, but they are independent outgrowths from the star-fish.body proper, instead of being prolongations of it, as in the common
The FEATHER-STARS, which include some of the rarest and most beautiful representatives of the group, are mostly inhabitants of deep water, and remarkable for the circumstance that either throughout life or in their early phases they are affixed to submarine objects by slender stalks. This peculiarity imparts to the animals such a flower-like aspect that, in conjunction with the indurated calcareous nature of their skeletons, they have received the title of their " Stone-lilies." This appellation, however, was originally more particularly applied to fossilised remains, which occur in remarkable abundance in the older geological strata. is the ROSY FEATHER-STAR, occasionally The most familiar British representative of the group obtained among seaweed in rock-pools on the southern coast, but more often brought up with the dredge from deeper water. In this form the elongate feather-like arms radiate from the central, relatively small, five-rayed body. There is no supporting foot-stalk in this adult stage, the animal being freely movable, and clinging to seaweeds and other objects by means of a cluster of claw-like filaments developed upon its under-surface. Releasing its hold upon its temporarily selected position, it can crawl about with the aid of the hooked extremities of its arms and their radiating joints. It can also propel itself through the water in a somewhat clumsy fashion by the consecutive flexion and extension of these appendages. This freedom of locomotion was not, however, always possessed by the feather-star. In its early days, and when of very small size, it was affixed to a slender foot-stalk, and dependent for its food on its extended the animalcules and other minute organisms which drifted or swam within reach of arms. The rosy feather-star takes its name from the bright rose-red tints by which it is usually characterised. Individuals of the species are, however, subject to considerable colour-variation. On the Australian coast, where many forms are abundantly represented, examples tinted deep crimson, black, bright golden yellow, or sundry admixtures of these several hues are not uncommonly found associated among a dredge-haul of these elegant sea-stars.
The PERMANENTLY STALKED STONE-LILIES are at the present day of rare occurrence. Up
Starfishes, Sea-urchins, etc. 749
to within comparatively recent years the so-called MEDUSA'S-HEAD LILY was, indeed, regarded as the only living representative of the group. This species has a pentagonal jointed foot-stalk that may be 3 feet long, with five slender appendages developed in whorls at short sub-equal distances throughout its length. From the shallow cup-shaped body at the apex of the stalk a tassel-like bundle of arms is developed, all of these being produced by repeated bifurcation from one of the five equivalent basal stem-joints. Dredging expeditions have within the.last quarter of a century revealed the existence of a considerable number of previously unknown species of stone-lilies in the abysses of the. ocean, a depth of no less than 3,200 fathoms representing the habitat of one such type. The Star-fish group is represented by the COMMON FIVE-FINGERS, or CROSS-FISH, as it is sometimes called, and includes a very numerous fkoto by N. Lazarnick] [New York. assemblage of species of varying size and shape STAR-FISH IN WATER. and colour. The British seas alone yield some of the five If pulled to pieces, each arms, or fingers, will grow into twenty forms. Among the more notable of these star-fish. a perfect is the SUN STAR-FISH, which, departing from the rule of possessing five arms only, has twelve or more, its contour, from which it derives its name, somewhat resembling that of a symbolic sun. The colours of this species are particularly brilliant, consisting usually of a variably patterned admixture of crimson, pink, and white. An extreme contrast in contour to the sun-star is presented by the so-called BIRD'S-FOOT species, in which the body is pentagonal and so flattened out as to somewhat resemble the foot of a duck. In the CUSHION-STARS the body, while pentagonal, is comparatively thick. The so-called SNAKE-ARMED SAND-STARS and BRITTLE-STARS constitute a section distinguished from the preceding by the character of the arms, which branch separately from the central body, and are composed of an innumerable series of calcareous joints, which snap asunder under the slightest provocation. The great majority of the species are provided with five simple arms only. In an exceptional form, however, known as the SHETLAND ARGUS, and its allies, these five arms, while simple at their base, bifurcate repeatedly and in geometrical progression to such an extent as to form in life a complex network of writhing, snake-like tendrils, that has been appropriately likened to a Medusa's head. It has been calculated that there are no less than 80,000-.,. terminal. arm-subdivisions in adult Photo by E. Connold.} [St. Leonards. examples of this species.. rr,.,,, STAR-FISH. OUT OF WATER, TURNING OVER. a, are there Sea-urchin Tribe the Amonff .,, The sucker-tipped tubes with which the star-fish effects loco-,, in this photograph.many notable departures from the typical form motion are well sbown