From Plant to Paradox, Rethinking the Sponge

“ And just as with the coral, it took Folks a long time to find out whether sponges were plants, shrubs, or insects.
Now it is decided that the sponge is an animal growth. And the same as with coral, the tiny creature that it starts from dies, and out from the skeleton, or frame, branches the sponge that sometimes grows very large, and sometimes is of a kind that remains small. One may be as big as a mop, others no larger than an egg. ”

“ The skeleton is nearly related in structure to silk, and this helped to settle the ancient dispute as to whether sponges were animal or vegetable. Their stationary life gave reason to the belief in their vegetable nature, while they multiply, like plants, by overgrowth and budding. They puzzled scientists for centuries, and one authority regarded them as worms' nests. In reality the sponge is a colony of little animals called polyps which occupy a sort of apartment house together, rearing families just as other animals do. ”

“ First division in the polyp group, the class Spongiaria has been created by scientists precisely for this unusual exhibit whose usefulness is beyond dispute. The sponge is definitely not a plant, as some naturalists still believe, but an animal of the lowest order, a polypary inferior even to coral. Its animal nature isn’t in doubt, and we can’t accept even the views of the ancients, who regarded it as halfway between plant and animal. But I must say that naturalists are not in agreement on the structural mode of sponges. ”

“ It may, then, be safely asserted that all naturalists are now satisfied of the animal nature of sponges, although they represent the lowest and most obscure grade of animal existence, and that so close to the confines of the vegetable world, that it is difficult in some species to determine whether they are on the one side or the other. ”

“ By night also it is on the look-out for scallops and sea-urchins. When it perceives a hand approaching it, it instantly changes its color, and contracts itself; when touched it produces a burning sensation, and if ever so short a time is afforded, makes its escape.
Sponges grow on rocks, and feed upon shell- and other fish, and slime. It would appear that these creatures, too, have some intelligence; for as soon as they feel the hand about to tear them off, they contract themselves, and are separated with much greater difficulty: they do the same also when the waves buffet them to and fro. ”

“ THE existence of the nests of corallines and lithophyta, and the mechanism of their polypi, made me conjecture, that it was the same with respect to sponges; that animals, nested in the interstices of their fibres, gave them their origin and growth: but I had not yet seen nor discovered the insects, nor observed their work. Sponges appeared to me only as skeletons: but I at length discovered these worms, which form sponges, in the four following species:
1. Spongia Americana tubo similis; The tube-like sponge of Plumier. 2. Spongia Americana longissima funiculo similis ”

“ Grant affirms, though in opposition to M. Cuvier, that the fibrous part of the sponge, which is insoluble in water, and forms a net work through every part of the body, is the skeleton of this zoophyte, serving, as in other animals, to give form to the body, and support to the softer organs.
“Sponge attaches itself sometimes to marine plants, so as to choak up their pores. Small bits of the same species will spread towards each other, and become one piece ”

“ In considering the various fisheries of the ocean, naturally that of the sponge, as one of the lowest forms of animal life, comes first in order. Science is hardly yet decided in its views concerning the organization and development of these obscure and complex creatures, and despite the investigations of modern naturalists, their position in the scale of animal life is still problematical, and their internal organization is still known only imperfectly. Dr. Bowerbank in his work on British Sponges, published in 1866, describes nearly 200 species, but this number by no means includes them all. ”

“ They cause it to follow its proper course, through and through the Sponge, and out again into the sea. On its way it loses the tiny scraps of food which it contains, and carries away any waste stuff out of the Sponge.
You will have noticed that there are various kinds of Sponges in the market; some are large and flat, others small and cup-shaped; some are soft, and others rather hard. They are all somewhat horny and elastic. This "spongy" material is the skeleton of the Sponge animal, cleaned and dried for your use. ”

“ Murren, sponges must be in a current after they have once taken hold. They can't swim around to get their food, so, like all the fixed forms of life, their food must come to them. If there is no current there is not enough food carried past for them to live on. If the current is too strong the sponge has to make an extra tough skeleton to brace itself against the rush of water and then it becomes too coarse for commercial use. Some of the polyps live on tiny animals with a lot of flint in their shells and the skeleton gets like glass. They call them glass sponges. ”

“ The sponges are the lowest of the many-celled animals. They consist of irregular masses of loosely associated cells, hopelessly anchored to the sea-floor. They represent the social instinct in embryo. The cells are but slightly specialised, and each cell leads a more or less independent existence. The sponge stands at about that stage of social integration and intelligence represented by those stupendous porifera which cover continents and constitute the ‘social organisms’ of the civilised world. ”

“ Under the microscope, these living sponge-units appear in various guises and shapes. Some of them are formless, and, as to shape, ever-altering masses, resembling that familiar animalcule of our pools we know as the Amoeba. These members of the sponge-colony form the bulk of the population. They are embedded in the sponge substance; they wander about through the meshes of the sponge; [pg 208] they seize food and flourish and grow; and they probably also give origin to the "eggs" from which new sponges are in due course produced. ”

“ In one Indian species, however, in which budding is unusually common (viz. Spongilla proliferens) , sexual reproduction takes place very seldom, if ever. It is not known whether the eggs of sponges are fertilized by spermatozoa from the individual that produces the egg or by those of other individuals, but not improbably both methods of fertilization occur.
The egg of a freshwater sponge does not differ materially from that of other animals. When mature it is a relatively large spherical cell containing abundant food-material and situated in some natural cavity of the sponge. ”

“ Budding as a rule does not result in the formation of independent organisms, but is rather comparable to the proliferation that has become the normal method of growth in sponges, except of course that individuality is much more marked in the component parts of a polyzoon colony than it is in a sponge. In the genera described in this volume budding takes place by the outgrowth of a part of the body-wall and the formation therein of a new polypide, but the order in which the buds appear and their arrangement in reference to the parent zoœcium is different in the [Pg 169] different groups. ”

“ If cells of two sponges of the same species are mixed it may be that they will recombine into the two original individuals—but this experiment never has been tried and would be quite difficult to interpret.
The sponge is the simplest, most primitive of metazoa, or many-celled animals. It acts as an individual, although there is apparently no central government, like a brain, controlling the behavior of the millions of individuals constituting the conglomeration. It ranges in size from organisms a fraction of an inch long, by far the most numerous, to masses several feet in diameter. ”

“ While the above view seems fairly satisfactory for the free swimming stage of the larval Sponge there arises in the subsequent development a difficulty which appears at first sight fatal to it. This difficulty is the invagination of the ciliated cells instead of the granular ones. If the granular cells represent the nutritive individuals of the colony, they and not the ciliated cells ought most certainly to give rise to the lining of the gastrula cavity, according to the generally accepted views of the morphology of the Spongida. ”

“ There is no current in the Atlantic, no distant sea, however narrow, but may send its contribution of richly laden sea water to the sponge's mouth. But not all the nitrogen, carbon, iron, that the tide bears is taken up by the sponge. It extracts only what it needs, what it can assimilate, and to most that passes remains, perhaps, insensible. So with our more complex organism—man. He, too, is set in the midst of oceans of sensation. Sounds, sights, odors, tastes, and touches flow round him in limitless variety. Of many, perhaps of most, he is never conscious ”

“ Such are the phenomena which in the various species of animals follow the removal of the true brain. Many of the acts are seemingly so purposive, and certainly so complicated, as to suggest that they must be conscious. It has, however, been shown that the fact that an act is apparently purposive and complicated does not prove that it originates in consciousness, and certainly in the brainless animal the past, present and future have been blotted out. ”

“ Men make use of something in nearly every branch of ocean life, from humblest to highest. The lowest of all, as I have already said, are the foraminifers; it is their skeletons which make up our common chalk. A close ally of theirs is the sponge, of which a dozen or so varieties are sold in the shops. Sponges come chiefly from the Mediterranean, the Persian and Ceylonese waters of the Indian Ocean, and from the Gulf coast of Florida. In the Old World they are obtained chiefly by diving. Men who are trained from boyhood to this work go out to the sponge-ground in boats on fine days. ”

“ In fact, we have a singularly instructive illustration of the process in the evolution of the sponges.
It is well known that the horny texture to which we commonly give the name of sponge is the former tenement and shelter of a colony of one-celled animals, which are the real Sponges. In other groups the structure is of lime; in others, again, of flinty material. Now, the Sponges, as we have them to-day, are so varied, and start from so low a level, that no other group of animals "illustrates so strikingly the theory of evolution," as Professor Minchin says. ”

“ The Jelly-fishes and their allies cannot be preserved as fossils, but some peculiar markings, at one time regarded as plants, are now supposed to be trails made by the tentacles of creatures of this kind moving over muddy bottoms. A few spicules indicate Sponges, and the ubiquitous groups of the marine Protozoa, the Foraminifera and the Radiolaunus, are represented by shells scarcely distinguishable from those of modern species. ”

“ The Sponges are a side-issue, or cul de sac, from the Protozoic world, and do not lead on to the higher. Each one-celled unit remains an animal; it is a colony of unicellulars, not a many-celled body. We may admire it as an instructive approach toward the formation of a many-celled body, but we must look elsewhere for the true upward advance. ”

“ For a certain proof that the conception of species rests on a subjective abstraction and has a merely relative value—like the conception of genus, family, order, class, &c.—no class of animals is of so much importance as that of the Sponges. In it the fluctuating forms vary with such unexampled indefiniteness and variability as to make all distinction of species quite illusory. Oscar Schmidt has already pointed this out in the siliceous sponges and keratose sponges ”

“ The sixty plates of figures accompanying this Monograph explain the extreme pliability of these small sponges “good species” of which, in fact, cannot be spoken of in the usual systematic sense. We find among them only varying series of forms, which do not even completely transmit their specific form to their nearest descendants, but by adaptation to subordinate, external conditions of existence, perpetually change. It frequently occurs here, that there arise out of one and the same stock different form-species, which according to the usual system would belong to several quite distinct genera ”

“ A delicate membrane often occurs outside this coat, but it is never thick or horny. The gemmules usually lie free in the sponge but sometimes adhere to its support; rarely they are fastened together in groups (e. g. in S. aspinosa, Potts) . The skeleton-spicules are never very stout and the skeleton is always delicate.
The species in this subgenus are closely allied and must be distinguished rather by the sum of their peculiarities than by any one character. They occur in all countries in which Spongillidæ are found. Seven Indian species may be recognized. ”

“ We are forced to conclude that current knowledge as laid down in the WPD is likely deficient in showing less than the actual diversity patterns of sponges. Many more areas remain to be explored and many recorded undetermined taxa remain to be named.
Global diversity of the Porifera.Numbers of sponge species recorded in each of 232 marine ecoregions of the world [19] extracted from the World Porifera Database (available: www.marinespecies.org/porifera, accessed 2011 Aug 31) . ”

“ Species combinations that do not fall under reasons 1 or 2 are considered accepted for the time being, unless they are known insufficiently to assess their genus affinity, in which case they are declared ‘species inquirenda’.
Sponge diversity Numbers of taxa tabulated
Based on the above considerations, Table 2 lists the numbers of WPD entries of species and lower-level combinations (varieties or subspecies) of the four recognized classes. So far (2011 August 31) the number of accepted species of Porifera is 8,553, the vast majority of which (83%) are Demospongiae (Fig. 9) . ”

“ On our theory the continued existence of lowly organisms offers no difficulty; for natural selection does not necessarily include progressive development; it only takes advantage of such variations as arise and are beneficial to each creature under its complex relations of life. ”

“ He is peculiarly struck with its failures to explain the infertility of hybrids and to fill the gap between the invertebrates and the vertebrates. After several years of independent study and investigation of the subject, he has published his conclusion in an elaborate article in the Medical Age that "the vertebrate organism, instead of being a single organism which has been evolved from a simple to its present highly complex form by a gradual and cumulative differentiation, is in fact a compound made up of two distinct organisms constantly associated ”

“ If anywhere truly exemplified in plants, it is only in the lowest and simplest, where the being is a structural unit, a single cell, memberless and organless, though organic,—the same thing as those cells of which all the more complex plants are built up, and with which every plant and (structurally) every animal began its development. In the ascending gradation of the vegetable kingdom individuality is, so to say, striven after, but never attained; in the lower animals it is striven after with greater, though incomplete success ”