Coral polyp

“ The coral polyp saturates itself with the lime-salts of the sea-water, much as the bone-corpuscles with those of the blood and lymph, and thus protects itself in life and becomes the flying buttress of a continent in death. ”

“ Indeed, the whole structure of a coral polyp is similar to that of an anemone, and we can now easily imagine the stomach of the polyp hanging down in the opening left between those delicate partitions. Coral polyps differ from sea-anemones, however, in three important ways—they have hard skeletons, they can not move about, and they usually grow in clusters. ”

“ The sea-anemones are wholly soft; they secrete no skeleton, or only the merest particles of hard matter. On the other hand, the coral-producing polyps secrete a stony skeleton. The old notion that coral is something built by an insect is entirely erroneous. The coral-producing animal is in no sense an insect, nor does it toil to build the clusters and reefs of coral which it forms. The coral-polyp lives and eats, and the getting of its food is the only labor of its life. ”

“ They cannot live at a greater depth than fifteen or twenty fathoms, and in defiance of the inclinations which rule human beings, they have the strongest distaste for sun and air; in fact, they die when exposed to it.
Now when the polyp dies its skeleton remains behind it, and millions upon millions of these coral skeletons make a layer of coral. These layers of coral gradually lift the generations of polyps upwards to the surface of the water. But as we have seen, the living polyps die when they get so far, and consequently the reef then spreads outwards. ”

“ It has power to deposit that carbonate-of-lime in solid masses.
But whereas the jelly-speck lives inside its shell, putting out tiny temporary limbs through holes for food, the coral-polyp more often lives outside its skeleton, clothing the dry bones with translucent jelly. This is rather more after the fashion in which man clothes his skeleton. Yet because of its make the coral-polyp cannot properly, in the full sense of the word, “secrete” or hide its internal framework.
It is hardly fair to speak of “the polyp” and of “it” in this connection. “Polyps” and “they” are more correct. ”

“ In that case it is quite likely that the coral builders might just keep pace with the subsiding foundations of their home, and build up a great thickness of coral rock during the countless years of change.
Sir Archibald Geikie has called attention to the swiftness with which the structure of the coral polyp's skeleton is effaced from the foundation and a compact mass of rock put in its place. The sea-water's chemical and dissolving action, and the vast amount of mud and sand produced by the breakers are chiefly responsible for this. As the rock is being formed it is always being cemented. ”

“ Some few even among coral-polyps live individual lives, but the greater number follow the community-system. This must always be looked upon as an inferior way of existence.
The most usual way in which polyps increase is by “budding”—not unlike the growth of a plant by buds. A small lump appears on one side of the parent, which increases fast in size, develops a mouth and tentacles, and by-and-by gives birth itself to other buds. The increase of numbers is enormous. One polyp may produce in a short time thousands or even tens of thousands of descendants. ”

“ The coral polyps and corallines are examples of colonies of this kind, possessing a common stalk which is formed as the process of multiplication goes on. In the case of coral polyps, the separate animals and the flesh connecting them secrete within themselves a hard, limy, supporting structure known as coral. In some species, the coral, or stony part, is so developed that the polyp seems to be inserted in the coral, into which it withdraws itself for partial protection (Fig. 45) . ”

“ Each coral polyp, a tiny marine animal that lives in enormous colonies, extracts calcium carbonate from the sea and exudes it to build a protective home around and above itself. Each generation of polyps dies in its protective home and each succeeding generation builds on top of its predecessor. ”

“ If we add to the labour of the Infusoria those of other creatures whose organization can only be discovered by the microscope, and take in the foraminifera, polyps, polyzoa, &c., we shall have to record still larger obligations to minute forms of living things. The coral polyp builds reefs that constitute the chief characteristic of certain regions in the Pacific ”

“ And as they build they form a barrier against the surf, inside of which, in water still as glass, the weaker and more delicate things can grow in safety, just as these very Encrinites may have grown, rooted in the lime-mud, and waving their slender arms at the bottom of the clear lagoon. Such mighty builders are these little coral polypes, that all the works of men are small compared with theirs. One single reef, for instance, which is entirely made by them, stretches along the north-east coast of Australia for nearly a thousand miles. ”

“ There are hills and valleys on the bottom of the ocean as well as on the land. We will fancy that some young coral polyps which have been swimming about in the sea settle on the sides of one of these hills, and begin to grow and spread all around it. They will increase also by the deposit of eggs until they form a circular wall.
As the coral wall grows, the lower polyps and the inner ones die, their skeletons forming a solid foundation for all that grow above them. There may be only about an inch of living coral on the outside of the reef. ”

“ When the polypes formed by budding or division remain associated, the polypidom is sometimes made up of nothing but an aggregation of these cups, while at other times the cups are at once separated and held together, by an intermediate substance, which represents the branches of the red coral. The red coral polype again is a comparatively rare animal, inhabiting a limited area, the skeleton of which has but a very insignificant mass; while the white corals are very common, occur in almost all seas, and form skeletons which are sometimes extremely massive. ”

“ A simple sea-anemone. Figs. 53 and 54. Young and fully developed colonial anemones. Figs. 55 and 56. Two views of a living coral polyp (Caryophyllia smithii) from above and from the side. The radial plates of limestone, conspicuous in Fig. 57, are seen through the transparent body wall. Otherwise the animal is like Fig. 52. (Drawn from living animal by H. C. Chadwick, A.L.S.) Fig. 57. The stony cup of Caryophyllia, seen from above and from the side, after removal of the polyp’s flesh. Plate XXV ”

“ The organ-pipe coral consists of lovely crimson tubes standing upright, and connected at short distances by thin flat plates, which give it the appearance of being several stories in height. These plates may be distinctly seen in Fig. 3. When alive, a little polyp protrudes from the top of each tube, and being of a bright purple color, it makes a striking contrast with the crimson tube.
Fig. 4.—Fragment of Red Coral with Polyps.
Red coral, which is used for jewelry, grows in a bushy form on rocks at the bottom of the Mediterranean and Red Seas. ”

“ When young, coral polyps are little jelly-like animals which swim about in the water. After they have chosen a resting-place, and the stomach and tentacles have grown, hard particles of lime, which they have drawn in from the sea-water, settle in their flesh to form a circular cup as well as the partitions inside. In this way the polyps soon acquire a solid frame, the soft parts being the stomach, the fringe of tentacles, and the fleshy mass covering the skeleton and the internal partitions. They can draw the tentacles entirely within the body, as the anemone does. ”

“ Strata of limestone, 2,500 feet in thickness, were accumulated in the ocean by the labours of Coral-polypes, allied to, but totally distinct from, those which had previously existed in the primary system. On the floor of a shallow sea, which then occupied the middle of what is now England, the coral reefs rose perpetually towards the day, atom by atom, the strata on which they were founded slowly and steadily sinking ever to a lower level, while successive generations of the industrious zoophytes wrought upwards, to maintain their position within reach of the light and warmth. ”

“ You will often hear coral spoken of as having been built by an insect, and you will see at once that this is far from correct. Coral polyps are very different from insects, and their skeletons grow, much as ours do, inside of the animal; so we can not say they have been built. All such animals as coral polyps, which have the mouth in the centre, with other parts radiating from it, are called "Radiates." ”

“ When the Coral polyps are not in an active state, or in other words, when they are not in want of food, these hydra-form polyps may not be visible, but being retracted into cells found as depressions in the skeletons of the Madrepores, they are lost to observation, and it is only when in quest of food and nourishment that their contractile tentacles are expanded, and distinctly prominent.
The physiology of the growth of the skeleton, both in the Madrepores and the Coral, is the same. ”

“ But it soon came out that that theory was not correct; for the coral polypes cannot live and build save in shallow water—say in thirty to forty fathoms. Indeed, some of the strongest and largest species work best at the very surface, and in the cut of the fiercest surf. ”

“ The specimens of corals which one sees in collections, or made into ornaments, are the calcareous skeletons of various kinds of the coral polyps. Some of the corals live together in enormous numbers, forming branching colonies fixed as closely together as possible, and secrete while living a stony skeleton of carbonate of lime. These skeletons persist after the death of the animals, and because of their abundance and close massing form great reefs or banks and islands. These coral reefs and islands occur only in the warmer oceans. ”

“ Not a single species, or even a single genus of those early strata, is identical with any that exists now. The Coral-polypes, for instance, while allied to ours, are quite distinct from them, though endowed with similar powers and habits, so that we may reason from analogy on the laws of their deposits. ”

“ When alive and in the water, coral polyps present a variety of beautiful forms and colors. Living polyps are composed of limestone skeletons covering and permeating a soft gelatinous substance which corresponds to the flesh of animals.246 When the polyps are removed from the water this soon decomposes and disappears; in certain species a part of it flows off as a thick liquid. ”

“ On the west coast of America, and on the corresponding coast of Africa, the currents of cold water from the icy regions which surround the South Pole set northward, and it appears to be due to their cooling influence that the sea in these regions is free from the reef builders. Again, the coral polypes cannot live in water which is rendered brackish by floods from the land, or which is perturbed by mud from the same source, and hence it is that they cease to exist opposite the mouths of rivers, which damage them in both these ways. ”

“ But there are certain parts of the world in which the coral polypes which live and grow are of a kind which remain, adhere together, and form great masses. They differ from the ordinary polypes just in the same way as those plants which form a peat-bog or meadow-turf differ from ordinary plants. They have a habit of growing together in masses in the same place ”

“ It is a great colonist, with no liking for a solitary life, but with, on the contrary, a great fancy for its neighbours; in fact, the polyps grow and thrive in clumps, and the clumps unite to form communities, and the communities increase to colonies and nations, till they unite to form what is called a reef. The coral polyps are rather exigent in the choice of their residential neighbourhoods. ”

“ But, strange as it may appear, the soft jelly-like bodies of the polyps give to the reef the power of resisting the billows.
The inner surface of the wall slopes gently to the land, and being washed by quiet waters often containing sand and mud, it is not favorable to the growth of polyps. Still, there are certain kinds of coral which thrive within the lagoons; some of them are exceedingly brilliant and beautiful. ”

“ Sometimes, at very low tide, if you have courage enough to risk being swept away by the breakers, going as far out on the reef as you can, you may catch a glimpse of them in their living state—great mounds and masses of what seems rock, but which is a honeycomb of coral, whose cells are filled with the living polypifers. Those in the uppermost cells are usually dead, but lower down they are living.
Always dying, always being renewed, devoured by fish, attacked by the sea—that is the life of a coral reef. It is a thing as living as a cabbage or a tree. ”

“ It has been a question with some naturalists, which part of a reef is most favourable to the growth of coral. The great mounds of living Porites and of Millepora round Keeling atoll occur exclusively on the extreme verge of the reef, which is washed by a constant succession of breakers; and living coral nowhere else forms solid masses. At the Marshall islands the larger kinds of coral (chiefly species of Astræa, a genus closely allied to Porites) “which form rocks measuring several fathoms in thickness,” prefer, according to Chamisso, [5] the most violent surf. ”