MARINE NATURE NOTES

Otago Daily Times, Issue 23044, 21 November 1936, Page 24

MARINE NATURE NOTES

Written for the Otago Daily Times By David H. Graham, F.R.M.S., ' • F.Z.S. > PLANT OR ANIMAL? .Since Labour Week-end I have, received quite a number of specimens of marina '-rowths which were collected by readers of this column and who wished to know more about them. These growths must have been collected at extreme low tide and comprised the following colours: Violet, orange, pink and grey, colours which are not usually found above low tide mark. All the correspondents fell into the error of calling their specimens “ pieces of plants found at low tide,” but in reality they were sponge growths and sponges are not plants, but animals, or rather colonies of animals, assembled in one individual body for their mutual well-being. Then again all snonges are not suitable for commercial use,, nor are they in their finished stage at all similar to when growing in the sea To begin with tliey are a yery low form of animal life, for their methods of reproduction are very plantlike. It may be a little difficult for my readers to accept the idea that sponges are animals. Even more so is this in the case of those sponges which grow more than a foot in length and which are so essentially plant-like in appearance that it seems a wide stretch of imagination to range them alongside the more familiar members of the animal kingdom. Growing on the stems of seaweed, on rocks and submerged piles, or on the shells of shellfish, or on the backs of crabs, they offer a striking resemblance to the weeds „hemselves. In shape some of them, as in the case of my correspondents’ specimens, may be merely incrustations on rocks, which simulate the vegetable slime commonly associated with the edges of sluggish streams. There is something distinctly quaint in the idea that a bath-sponge should have once been a living creature. or a living colony of creatures, elegant in form, richly coloured, and pulsating with life. Two thousand years ago Aristotle was convinced of the animal nature of a sponge, and succeeding generations of scientists have been sorely confused as to its relationship with the rest of the animal kingdom and inanimate nature. It was in the eighteenth century the celebrated John Ellis proved to his own satisfaction that a sponge was not only a living crea tore, but an animal into the bargain blit it was not until the nineteenth century that all scientists and naturalists were convinced he was correct.

The skeleton of a bath sponge consists of a continuous close-meshed network of silky fibres, soft, resilient, and pleasant to touch. In spite of its lowly position in the scale of animal life, the structure is very complex The material which composes a sponge may be divided into two sections, the outer or flesh part and the inner or fibrous part. The body tissues are composed of various kinds of cells, some of which assist in the process of nutrition, while others are employed in developing the fibrous skeleton, and others again form a kind of lining to the body substance Other sponges are made up of a skeleton of minute needles of silica known as spicules, about a tenth to a third of a millimetre in length, pointed at each end, arranged, not in a continuous network, but loosely articulated and readily separated. Very marvellous is the diversity of form to be found in the spicules. They are to be found scattered through the bulk of the sponge, sometimes as a single particle, in

1 other cases, hooked one into the other to form a complete flinty framework. It has probably never occurred to s many of us that we get into our s baths in company with a skeleton; these fibrous bath sponges are the whitened bones, of a living thing. The sponge that the reader uses—unless, of course, he or she prefers the flaccid rubber substitute that is ■ attempting to oust the natural ; article—was at one time covered • with flesh. It was a yellowish, 1 brownish, or dark purplish object, ; smelling faintly like garlic, elastic > and slightly slimy to the touch; in i fact, living bathroom sponges have been compared in colour and consistency to a fresh liver There is nothing very suggestive of a living thing about a domestic sponge, and yet when it is examined with care it reveals a high degree of organisation. The holes that riddle jt are of various kinds; there are conspicuous round holes, often large enough to admit the finger, and leading into neatly trimmed, more or less straight cylindrical shafts that sink into the substance, and there are smaller holes leading into a labyrinth of passages some of which open on to the main shafts. There are two methods of reproduction in a sponge. There is the sexual method; the male sperms are tiny cells with short, blunt, stiff tails, and the female eggs are giants in Comparison. Fertilisation results ir. the formation of a ciliated larva that swims away, settles down somewhere else -md. develops into a new sponge. A single sponge will produce thousands of eggs and sperms in a season, and, taking all things into consideration, the surprise is that they do not over-run the sea with growing sponges. Presumably the percentage of eggs and sperms lost by accident must be very high indeed On placing a few of the fertilised eggs of a sponge, which, in J size and shape, might not inaptly be compared to a small pin’s head, in a watch glass containing sea water, it will soon ecome evident, even to the naked eye, that they are able to swim with considerable facility; but how they managed to accomplish such a feat is by no means so easily discernible On examining them under a microscope, the machinery employed becomes revealed to. sight, and certainly a spectacle 1 more wonderful imagination scarcely could conceive Hundreds of paddles furiously at work, are studded over the surface of these tiny seeds, so rapid in motion that the eye almost refuses to perceive their shape. A sponge has great powers of reorganisation. A small piece of living sponge cut away from the parent will live and grow, and indeed, if it is put through a fine gauze, the separate parts will come together again, or if not able to come together will continue to grow into a mature sponge, for the parts of a sponge are not differentiated into organs, and a fragment a twelfth of an inch i across would contain all the differ- ; ent kinds of tissue that form a sponge. A sponge is made up of 1 pores or canals, and a careful examination will show the use of these pores; they will be seen to i allow the passage of minute streams < of water, which pass through diverse ’ channels and passages until they meet in a central hollow and pass ; out in one continuous'stream But 1 the water that passes away has been < changed; it has been deprived of 1 the minute particles of matter which 1 were held in it, and it has also ex- 1 changed its oxygen for carbonic acid t gas. To obtain this matter needs c a most elaborate system on the \ minutest scale possible. The late t Professor Huxley summed up the f nature and organisation of a living t sponge in one short paragraph, t which is well worth quoting. He 1 described it as “ a kind of sub- i aqueous city, where the people are 1 arranged about the streets and roads | I

in such a’ manner that each can easily appropriate his food from the water as it passes along.” It is strange to reflect that in sponges we have a group of animals, widely spread over the face of the earth, that have persisted from the beginning of time, almost unchanged in form and in habit, and leading a life so negative in character that it is difficult to see what contribution they make to the world; they prey on nothing, except those which invade their waterways: preyed upon by nothing, they spend their lives pumping water, in which they live quietly, through their bodies. Their greatest contribution is, of course, our domestic sponge, but even that is being superseded by rubber substitutes.