Transactions of the Asiatic Society of Japan/Series 1/Volume 1/The Hyalonema Mirabilis
THE HYALONEMA MIRABILIS,
BY
HENRY HADLOW, Surgeon, R.N.
Read before the Asiatic Society of Japan,
on the 30th, October, 1872.
———o———
The Glass Plant, Glass Coral, or as it is now more generally and more correctly termed, the “Glass Rope Sponge” of Japan,—Hyalonema Mirabilis, as it was christened by Dr. Gray, and is termed by systematic writers,—is tolerably familiar in appearance to most residents in the East, cither in its complete form, in which it presents a spongy expansion, sometimes large, sometimes small and of variable shape, having springing from it a very beautiful twisted coil of vitreous-looking cords, which itself is, for a part of its extent, invested and covered by a brown, warty bark-like structure; or as, perhaps, it is more commonly met with, in an imperfect condition, presenting only the glass rope and its attached bark without any trace of the spongy expansion from which it has probably been torn. We also sometimes meet with portions of the glass coil most ingeniously attached to and grouped with corals, shells and other marine products, which I need only refer to to remind you that such arrangements are entirely artificial, notwithstanding that they are often so artistically done as to have a most deceptively natural appearance, and that the way in which the coil is placed, with the free ends of the plume upward, has had, I imagine, considerable influence in persuading people that that was its ordinary mode of growth.
The Hyalonema has long been a favourite with collectors from the intrinsic beauty of its form, whilst to the student of marine zoology it has a special interest from the peculiarities of its structure, the doubt that obtained as to the precise position it occupied in the animal kingdom, and from an uncertainty, not even yet definitely set at rest, as to the true relation which the parts of which it is composed, namely, the sponge head, the glass rope, and the so-called bark or polythoa, bear one to another.
Dr. Gray, who described the Hyalonema from some of the early specimens and gave it its scientific name, regarded the glass rope and its bark-like enveloping polythoa as an organism entirely independent of the spongy mass to which it was commonly found attached, and the glass rope with its coriaceous investment were described together as barked coral, the silicious twisted stem or axis being looked upon as the foot selection or sclero basic corallum, as it is termed, of the compound polyp mass investing it and forming its bark. Dr. Gray considered its attachment to the sponge as merely parasitic and accidental, the sponge being supposed to form a fixed base from which the Hyalonema grew and projected like a plume. In a very trustworthy little work by Professor Reay Greene published in 1863, the Hyalonemas are referred to the Actinozoa, although provisionally, and since that time our knowledge of them has increased. In 1868 it was reported that Hyalonemas had been discovered in the deep sea dredgings at Setubal on the coast of Portugal. It was first supposed that these must have been thrown overboard from some passing vessel returning from Japan, but other fresh specimens followed and it became certain that the Hyalonema was a denizen of Portuguese waters. Since that time the deep sea dredgings of Setubal, carried on at depths of 300 and 400 fathoms, have been a kind of happy hunting-ground for marine zoologists. A fine collection has been secured for Lisbon. Professor Percival Wright was successful in finding specimens, some living, and some of large size, and has shown us that our original opinions were founded in mistake, and that so far from the sponge being the fixed mass it is the glass rope which dips deeply into the mud or sand and forms a kind of anchor for the sponge head, probably being secreted by it for that purpose, and that it is not a mere growth attached parasitically to the sponge, but an essential part of its constitution. Professor Wyville Thompson has also been engaged in the capture and study of these forms, and has promised a memoir on the genus which is impatiently looked for by all interested in the subject. I have, not, however, heard of its appearance yet, and in the mean time, there are many points of interest and many structures of great beauty which we can discover for ourselves with a little expenditure of time and patience.
The sponge mass of the Hyalonema is perhaps most commonly cup shaped, with the glass rope attached to its inner concave surface. Sometimes it is more or less globular, with the glass rope running through it and attached to nearly the whole length of the long axis. As you see in the specimen before you, it is sometimes of considerable size, eight or nine inches in its longest diameter. It must be remembered that in a dried specimen such as those before us, just as is the case with the common sponge of our toilet table, what we see is the mere frame work or skeleton of the actually living sponge. During the life and growth of the sponge this skeleton is clothed with a soft semi-fluid gelatinous coating called sarcode, which is the really truly living matter of the organism; by which it breathes, by which is takes its food, by which it propagates and multiplies its species, and by which the skeleton, and the spicules of which I shall have something to say hereafter, are formed and secreted. Time will not admit of our discussion of this sarcode matter. I can only stay to remind you that it is not a mere homogeneous layer like a stratum of jelly, but that it contains an immense number of small sarcode cells or amœboid bodies, more or less globular in shape, often provided with a long whip-like filament or flagellum, by whose lashing movements currents of water are kept circulating over the little sarcoid for its aeration and nutrition; and, lastly, that each little sarcoid has an independent vitality which enables it to live when separated from the parent mass, and under favourable circumstances to become the commencement of fresh sponge growths. Also the living sponge presents an aquiferous system, consisting of a series of anastomosing channels passing through its mass, through which currents of water are constantly passing, entering by the minuter orifices or pores, and escaping from the larger openings or oscula, in this way bearing floating nutritive material to the fixed sarcode matter and at the same time aerating the whole animal. Such are the general characteristics of living sponge; the skeleton which we see in dried specimens is, in the ordinary sponge of every day life, composed of horny material in form of tubes, in composition resembling animal matter, and of a softness and elasticity which gives it its domestic value. These sponges are called keratose or horny, and form one of the three groups into which sponges are divided by the nature of their skeleton. In a second order the framework is calcareous, composed of carbonate of lime, and there is yet a third to which Hyalonema belongs in which the skeleton is silicious. Whatever may be the composition of the fibres forming the framework, they are arranged always in an intricate network, thus securing the peculiar cellular structure which sponges possess. For the purpose of strengthening the skeleton and assisting in giving support to the semi-diffluent sarcode matter, we also find, especially in the calcareous and silicious sponges, what are termed spicules, that is, calcareous or silicious particles of definite form, generally slender, acicular, sometimes needle-like in shape, in other cases assuming very graceful and elegant forms. The Hyalonema is particularly rich in these, but as we shall have to return to them in speaking of the polythoa or bark, it will be convenient to consider them then.
So far we have met with little in the general formation of Hyalonema different from siliceous sponges generally, nothing indeed, except the variety of beauty of the spicules which we shall describe presently, but the glass coil or glass rope is a structure altogether new. As we have already seen, it was originally thought not to be a portion of the sponge at all, but the foot secretion of an Actinia. It is now more commonly regarded as an integrant part of the sponge itself, chiefly from the fact that we have recently become acquainted with several other sponges similarly provided with foot pieces or stalks serving as bases of attachment. We may, if you please, look upon the glass cords, as kind of gigantic spicules dipping down into the soft mud and ooze, and serving as an anchor. If we take a single filament of the cord and examine its structure, we find that it is not homogeneous as the thread of spun glass would be to which it has been compared, but that it is laminated,—composed of layers upon layer of silicious matter deposited round a central axis. This can be seen without much difficulty by breaking the glass fibre across in such a way as to produce an irregular splintered fracture, and examining the broken end under a low miscroscopic power. The appearance presented is shown in the sketch, taken from an object laid on the table, and in the original it is easy to count more than twenty layers entering into the composition of the fibre. Towards each extremity of a fibre the number of layers is fewer and the fibre consequently tapers off, and as the fibres themselves do not extend the whole length of the coil, this likewise tapers off in the end which is attached to the sponge, and appears there to be tough and fibrous and securely attached to the spicules and network forming the skeleton of the sponge mass.
Mr. Carter in his very interesting observations on the development of the fresh water spongilla has described how the spicula of that organism are formed. He has shown that they first appear as a delicate line enclosed and developed within an elongated sarcode cell, and that they grow rapidly by external additions until they attain their full dimensions, soon outgrowing the cell in which they first appear. There can be little doubt that the filaments of the glass rope are developed in some more or less analogous way, and that in the living state they are, like the silicious skeleton of the sponge itself, clothed with sarcode matter from which layer after layer of silicious material is deposited as long as the fibre continues to live and to grow.
If we now exame the coriaceous envelope of the glass coil, or polythoa, which can be most easily done in dried specimens after it has macerated for a few days in water, we can easily make out that it consists of two layers, an inner one closely connected with some of the fibres of the glass rope, and which has been stated by some observers to extend between and invest each individual fibre of the glass coil which forms its axis;—I am, however, doubtful if this is the case; it does not appear to be so in the large specimens on the table;—and an outer thicker one which is largely made up of small particles of sand, broken shells, minute foraminiferæ, and here and there a diatom, mixed up with the beautiful spicules secreted by the organism itself. At first sight it reminds one of the little tubes which the terebellas build up from sandy and shelly particles and which you often meet with cast up on the sea shore. Studded about on the bark are little wart-like projections with flattened crowns, having in the centre a small depression or orifice with little radiating grooves proceeding from it. If, in a macerated specimen, we make with a sharp knife a thin section from without inwards, taking care to include the central depression, and then examine it with a common lens, we shall observe, supposing our section to have been a tolerably successful one, much the appearance which you see drawn here, the original of which is on the table. We see that the innermost of the two layers of the bark passes under the little cup-like projection, all together forming the base of the included cavity; whilst the thicker external layer, separating from the inner one, is raised up, forming the wall and crown of the tubercle until it. reaches the central depression, where it turns inwards, forming a small funnel-shaped process which opens into the general cavity of the structure. This at once reminds us of the formation of the Actinozoa, which consists of a simple digestive, or stomach tube, open at both ends, and suspended in the centre of the polyp by little partitions called mesenteries; indeed, the resemblance to an ordinary zoantharian is so close that we cannot feel any surprise when Dr. Percival Wright tells us that in living specimens brought up from the deep-sea soundings at Setubal, he has observed the little wart-like projections of the bark expanding their tentacles in search of food just like the common sea anemone of our aquaria, or any other zoantharian. It is a compound polyp; that is, although each little nipple-like projection has its own digestive sac, and its own prehensile organs or tentacles by which it secures its own food, they all unite together to contribute to the growth of the compound mass of which they form part. Such being the case, it is clear that the polythoa, or coriaceous investment of the glass rope, must be an organism totally distinct from the sponge mass, whose nutrition we have already seen to be derived from the currents of water flowing through its aquiferous channels. If we admit the silicious stem or glass rope to be an essential part of the spongy portion, we shall be constrained to regard the polythoa as a mere parasitic investment, and having no structural relations with the sponge and its glass coil at all. There are still, however, some observers who consider that from the universality with which the bark is found coating the glass rope and no where else, and from its containing peculiar silicious spicules, that these two, the polythoa and glass rope, form one organism which may exist independent of the sponge at all, as was first supposed, and they consider such specimens as these, in which no trace can be discovered of the spongy expansion, and the glass coil is coated to its extremity with polythoa, as strongly favouring this belief. It is perhaps premature to pronounce dogmatically either way, although the first of these views—that is, of the parasitic nature of the polythoa—meets with almost universal acceptance.
What, then, are these spicules of which so frequent mention has been made? They are easily obtained for examination. If we put a few particles of the polythoa, or some fragments gently torn from the inner surface of the sponge, into strong nitric acid for a day or two, the animal and extraneous matter will dissolve away, and the silicious particles, including the spicules, will alone remain. These must be well washed in many waters to remove all traces of the acid, and will then be ready for examination with the microscope, or for mounting in Canada balsam, if it is desired to keep them as permanent objects; taking care in the latter case, not to break the more delicate forms by too much pressure on the covering glass. Proceeding thus with the polythoa, we find that the spicules have a great tendency to assume the cruciate form, the most common of all being described in scientific terminology as cylinuro-cruciform with densely spiculete shafts. In some other forms, the shafts of the cross are spiculate only at the extremities, and are much more delicate in contour. We meet with others in which the lateral shafts of the cross are reduced to mere rudimentary projections, whilst still in others they are absent altogether and the spicule is a short thick cylinder studded all over with sharp spines. Of these straight or nearly straight spicules we find several kinds, some spinous only at the ends, others with a small central enlargement, and lastly we meet with delicate spicules, some in the form of crosses presenting perfectly smooth outlines. In the sponge, some of the commonest, although not the most striking, forms, are these spiculated cruciform spicules, with a little foot-piece in the form of a cross from which springs a much spiculate stem. Dr. Wright tells us that these are chiefly found round the oscula or openings of the aquiferous channels and lining the cavities of the sponge, attached by the little foot piece to the sarcode mesh. He says,—to quote his own words—“From the peculiar way in which they are placed on the edges of the meshes, and from the fact that the barbs on the stem of the spicules all point in one direction, it is possible that while it would be easy to glide over the slimy sarcode down into an osculum, return would be no easy task, as any solid body would be at once caught and retained by the barbs.” It is, however, only in fresh specimens, or in those which have been at once put up in preservative, that these can be properly seen in their natural position; in the dried sponges they are so loosely attached as generally to become separated.
Amongst other forms to which we can only briefly refer, are many of delicate cruciform shape, much resembling the foot pieces of the spicules last described. Some are large and present the appearance of four radii springing at right angles from a central axis, hexradiate. We also find a number of peculiar kedge-like forms, some very simple, others larger, passing through various gradations of size, but leading up to the magnificent spicule described in scientific terms as “multihamate birotulate, shaft slight, cylindrical, papillate.” It might be roughly compared at first glance to two open umbrellas made of the finest spun glass with their sticks fused into one, but the true structure of the expanded portion is shown here, delicate silicious leaves curving gracefully from each extremity of the shaft towards its centre.
There are many other forms of spicules to reward the painstaking microscopist who searches for them, some of them minute and requiring the higher powers of the instrument and careful examination of the lighter washings, but the most beautiful and distinctive are those which we have seen and which can be easily demonstrated with the most ordinary microscope.
In conclusion, I would venture to impress upon you that there is a great deal yet to be discovered concerning this very interesting and curious sponge, which can only be learned by the careful examination of fresh specimens in the natural condition in which they are brought up from their ocean bed, and it is chiefly with a view of enlisting amongst the ranks of the observers any of my hearers who may be passing a holiday at Enosima or the neighbourhood from which the sponges are brought, that these few brief notes of the Hyalonema are brought before your notice. The discovery, for example, of a young specimen complete in sponge head and glass rope, but without the coriacaous investment, would be of the highest scientific value. The verification of the observation that the little warty projections of the bark have their own tentacles and their own mouths, would have its interest, and the discovery of the bark-like polythoa, coating other structures altogether apart from the glass rope, would all aid us in clearing up matters yet in doubt, and help to give us a clearer view of the very interesting but not yet fully understood Hyalonema Mirabilis.