Holothurian

“ If, now, we compare these animals in the various attitudes natural to them, we may fail to recognize the identity of parts, or, at least, it will not strike us at once. But if we place them all—Holothurian, Sea-Urchin, Star-Fish, Ophiuran, and Crinoid—with the oral or mouth side downward, for instance, we shall see immediately that the small area at the opposite end of the Holothurian corresponds to the area on the top of the Sea-Urchin; that the upper side of the Star-Fish is the same region enlarged; that, in the Ophiuran, that region makes one side of the small circular disk ”

“ We have seen that the Sea-Urchins approach most nearly to the sphere, and that in them the oral region and the sides predominate so greatly over the ab-oral region that the latter is reduced to a small area on the summit of the sphere. In order to transform the Sea-Urchin into a Holothurian, we have only to stretch it out from end to end till it becomes a cylinder, with the oral region or mouth at one extremity, and the ab-oral region, which in the Holothurian is reduced to its minimum, at the other. ”

“ Polyzoa were numerous. I noticed representatives of the genera Retepora, Crisia, Eschara, Cellepora, Lepralia, and Myriozoum. There were also some examples of Sertularia and other flexible hydroids.
Our gropings over the platform of fringing reef, which formed the foreshore at low water, resulted in the acquisition of several species of holothurians. Among these was a large Synapta, which was abundant, and a very tough-skinned holothurian—of the genus Moliria—provided with organs resembling teeth at its posterior extremity. ”

“ Just as in the case of the little curved or -shaped spicules, formed apparently within the bounds of a single cell, so also in the case of the larger tetractinellid and analogous types do we find among the Holothuroidea the same con­fi­gur­a­tions reproduced as we have dealt with in the sponges. The holothurian spicules are a little less neatly formed, a little rougher, than the sponge-spicules; and certain forms occur among the former group which do not present themselves among the latter; but for the most part a community of type is obvious and striking (Fig. 216) . ”

“ Pentactaea Theory.—In opposition to the calycinal theory has been the Pentactaea theory of R. Semon. There have always been many zoologists prepared to ascribe an ancestral character to the holothurians. The absence of an apical system of plates; the fact that radial symmetry has not affected the generative organs, as it has in all other recent classes; the well-developed muscles of the body-wall, supposed to be directly inherited from some worm-like ancestor ”

“ Representatives of nearly all the great divisions of the animal kingdom which occur in the sea are found in the depths. Protozoa, sponges, cœlenterata, round-worms, annelids, crustacea, polyzoa, brachiopoda, molluscs, echinoderms, ascidians, fishes, crowd the sea-bottom. The Valdivia has brought home even deep-sea ctenophores and sagittas, forms hitherto associated only with life at the surface. The same{33} expedition also secured adult examples of the wonderful free-swimming holothurian, Pelagothuria ludwigi, which so curiously mimics a jelly-fish. ”

“ That they have selection-value in their present perfected form is beyond all doubt, since the animals are enabled by means of them to bore rapidly into the ground and so to escape from enemies. We do not know what the initial stages were, but we cannot doubt that the little improvements, which occurred as variations of the originally simple slimy bodies of the Holothurians, were preserved because they already possessed selection-value for the Synaptidae. ”

“ Ambulacral appendages take the form of: (1) circumoral tentacles, (2) sucking-feet, (3) papillae; of these (1) alone is always present. The gonads are not radiately disposed.
The comparative anatomy of living forms, combined with the evolutionary hypothesis sketched above, suggests that the early holothurians possessed the following characters: subvective grooves entirely closed; 5 radial canals, proceeding from the water-ring, gave off branches furnished with ampullae to the podia on each side of them, the 10 anterior podia being changed into cylindrical tentacles ”

“ But a Swedish observer, Oestergren, has recently shown that they have a biological significance: they serve the footless Synapta as auxiliary organs of locomotion, since, when the body swells up in the act of creeping, they press firmly with their tips, which are embedded in the skin, against the substratum on which the animal creeps, and thus prevent slipping backwards. In other Holothurians this slipping is made impossible by the fixing of the tube-feet. ”

“ The highest of our Holothurians in structure, is the Pentacta. (Fig. 130) It is very rare on our beaches, though occasionally found under stones at low-water mark; farther north, in Maine, and at Grand Manan, it is very common, covering all the rocks near low-water mark. It is a chocolate brown in color, and [Pg 100] measures, when fully expanded, some fifteen to eighteen inches in length. Unlike the Cuvieria, the ambulacral suckers are evenly distributed and almost equally developed on all the tubes ”

“ The first paper on Middle Cambrian fossils from British Columbia included the description and illustration of some new types of Merostomes. [1] This paper contains a preliminary notice of the discovery of certain forms of Holothurians and one new Medusa. ”

“ The body of this strange creature presents the form of an elongated and [292] worm-like cylinder; its dimensions are so variable that, while some species are only an inch or two in length, others attain thirty and even forty. In general, the skin of the Holothuria is thick and leathery; it includes muscles, and is armed occasionally with small projecting hooks or fangs, which enable the creature to hang for a few seconds on to foreign bodies. From this coriaceous envelope issue tentacular feet analogous to those described in the sea-urchin and sea-star. ”

“ But, with these several advances toward the worm type, the hereditary disadvantages of the Holothuroid act as impassable restrictions to any great development. The organs of the higher senses are wanting. It is in no way adapted to swimming, its exterior organs being quite unfitted to develop into fins. ”

“ J. Allan, of Forres, who has enjoyed the best means of observation, informs me in a letter that the Holothuriæ (a family of Radiata) subsist on living coral; and the singular structure of bone within the anterior extremity of their bodies, certainly appears well adapted for this purpose. The number of the species of Holothuria, and of the individuals which swarm on every part of these coral-reefs, is extraordinarily great; and many shiploads are annually freighted, as is well-known, for China with the trepang, which is a species of this genus. ”

“ Like that leviathan chosen by the Almighty, in an age long subsequent, as an illustration of His power and greatness, the holoptychius must have been king over all the inhabitants of - 134 - the sea, and the magnificent language of Job, descriptive of the living animal, applies not less graphically to the extinct one: "Who can open the doors of his face? his teeth are terrible round about. His scales are his pride, shut up together as with a close seal. One is so near to another, that no air can come between them. He maketh the deep to boil like a pot: he maketh the sea like a pot of ointment. ”

“ A Holothuria is very unattractive in appearance when lying listless upon the sea-beach, but if a small specimen be transferred to the aquarium, it exhibits features of a very singular and interesting character. When about to change its position, the head, hitherto concealed, is protruded and expanded, until it assumes the form of a beautiful flower.
The animal moves principally by aid of sucker-like feet, similar in form to those of the Asteriadæ, or Sea-Urchins. In most species, the body is divided longitudinally into five rows of suckers. ”

“ If, then, Asteroidea are the most primitive Eleutherozoa, we may imagine that primitive Echinoidea were derived from Asteroidea through adaptation to life in crevices, where an upward bending of the radii was of advantage, in order to enable the animal to attach its podia above as well as below itself; and that Holothuroidea arose from primitive Echinoidea in which the plates of the corona were still movable, through a further adaptation to narrow crevices, where worm-like wriggling would be the most successful method of adapting themselves to their environment. ”

“ The only fossil remains of Holothuroidea consist of isolated ossicles—wheels, gratings, anchors, etc.—which first make their appearance in the Carboniferous limestone and tell us practically nothing of the evolution of the group. From a comparison with one another of the living families, certain conclusions can be drawn. The Aspidochirote feeler and the method of using it recall forcibly the shape and function of the buccal tube-feet of Spatangoidea. ”

“ It has been cut into two pieces, and each of these species becomes a new being.
Plate X.—Fishing for and curing the Holothuria in the Indian Ocean.
The habits of these animals are but little known. They inhabit the seas, and are spread over every latitude. Their very limited movements consist in a kind of reptation or crawling motion, produced by the undulations of their bodies or by the contractions of their feet. Holothurias are generally found in the act of creeping upon stones or on portions of submarine rock, but always in sheltered places, for they appear to dread the action of light. ”

“ There are about 520 species of living Holothuroidea, and of these about twenty-one have been recorded from British waters. One of the best-known of the British species is Holothuria nigra (Fig. 254) , commonly known as the "Cotton-spinner"; and this we shall take as a type for special description. The animal may attain a length of a foot when fully extended, and has a diameter of from 3 to 4 inches. It is of a very dark brown colour on one side, which in crawling it keeps uppermost, whilst on the lower side it is of a tawny yellow hue. ”

“ On the present occasion he is unusually elated, for he has made the discovery of a Holothuria with twenty tentacula, a species of the Echinodermata which Professor Forbes, in his book on Star-Fishes, has said was never yet observed in the British seas. It may be of small moment to you, who, mayhap, know nothing of Holothurias: but it is a considerable thing to the Fauna of Britain, and a vast matter to a poor private of the Cornwall mounted guard. ”

“ Holotypes - each the single specimen of a species that is used to define the characteristic features of that species. Holotypes exist as a physical object carefully protected from damage through handling. Digital colour 3D models of sufficient detail will enable collections managers to liberate these precious specimens for the research work they are intended to fulfill. ”

“ It must be admitted that this is a strange mode of evading its enemies: the soldier rarely throws his arms away in the moment of danger! But the Holothurias possess a wonderful recuperative power also; and it is probably quite conscious, when it thus empties itself to disappoint its pursuer, that it can promptly replace the organs which it has voluntarily parted with.
Dr. Johnston relates that he had forgotten for some days to supply a Holothuria with a change of water. The creature, in consequence, ejected its tentacles, its buccal apparatus, digestive tubes, and a portion of its ovaries. ”

“ In truth, no two organisms have ever been so maltreated; and if the reader will kindly bear with me a little further, it will not be difficult to show him that the holoptychius had peculiarities of its own quite as distinct as those that have come before us in the megalichthys, and that each animal has a full and legitimate claim to a separate and independent niche in the gallery of fossil fishes. ”

“ Cystidea, Crinoidea, Blastoidea, Asteroidea, Ophiuroidea, Echinoidea. As for Holothuroidea, the fossil evidence allows us to say no more than that the class existed in early Carboniferous times, if not before. The second method is to work out by slow and sure steps the lines of descent of the different families, orders, and classes, and so either to arrive at the ancestral form of each class, or to plot out the curve of evolution, which may then legitimately be projected into “the dark backward and abysm of time.” ”

“ The body-wall of the Holothuroidea is strong and muscular, and is strengthened by the presence of numerous spicules of carbonate of lime, often in the form of little anchors, wheels, and crosses, while the outer surface is rough and slimy, and often of a colour so closely resembling the surroundings of these animals that they are not easily observed. This feature is one of great value to the creatures, since they have no means of defence from their enemies, and seem to owe their safety entirely to their protective colouring. ”

“ Holothuroidea with shield-shaped feelers provided with ampullae; with radial canals and numerous podia and with respiratory trees. Retractor muscles absent. Nearly a third (158) of the species of Holothuroidea belong to this order, but there are only six genera, and of these Holothuria includes no less than 109 species. The Aspidochirota seem for the most part to live on somewhat firm ground, the surface of which they are continually sweeping with their shield-shaped feelers, which brush the adherent organisms into the capacious mouth. Four species of Holothuria—viz. ”

“ Turning now to the question of the origin of the classes of Eleutherozoa, we find that the study of development strongly reinforces the views gained from the study of adult anatomy. The Asteroidea are the most primitive group; only in their case {622}is the fixed stage retained, and both Ophiuroidea and Echinoidea pass through an Asteroid stage in development. The only serious competitors for the position are the Holothuroidea, which many have imagined to have been directly derived from Cystoidea (in the old sense; better Thecoidea) . ”