Sponges are fascinating!

Sponges are very common, yet few of us pay them much attention when we are looking at organisms on the shore. It may be because they are primitive animals that don’t move, yet they are fascinating and, whether large or small (and they come in many shapes and sizes), they reward close examination. Some examples can be seen in the above image taken by Dan Bolt (from the BBC website) and those interested in examples of sponges from around the coast of Great Britain are recommended to view the excellent images taken by Dr Keith Hiscock and available on the MarLIN website [1].

Philip Henry Gosse writes about sponges in Land and Sea [2], in a chapter headed “An Hour among the Torbay Sponges”, and this has a special appeal for me as I am very familiar with the coast of that bay. Indeed, his collecting of sponges centred on the rocky outcrops at Goodrigton (above), a favourite haunt of mine as a boy [3]:

Diverse as they are in form, and in texture, and in colour, and in manner of growth, they have all the same essential structure. We cannot learn much about them by looking at them here, especially after they have been for an hour or more forsaken by the receding tide; but if we take one or two specimens off very carefully, so as not in any wise to bruise or break their delicate organization, separating, in short, by means of the chisel, a bit of the rock itself on which they are growing, and, committing them to a jar of sea-water, examine them at home, we shall find much to admire..

This is typical of Henry Gosse’s approach to observation and he was a populariser both of the use of aquaria and of microscopes to study living organisms. Nowadays, however, we might frown at Henry’s use of a hammer a chisel to acquire specimens in situ. In Land and Sea [2], Gosse continues that:

..each has then been rinsed and deposited in a small glass cell with parallel sides, full of fresh and clean sea-water, and left for twelve hours at least. Then, taking care not to touch the glass cell, nor to jar even the table on which it is placed, either of which might cause the sensitive sponge instantly to cease its operations, we bring a powerful pocket-lens close to the glass, and intently watch the specimen within. Suppose it is one of the yellow species, which throws up little hillocks, the Crumb-of-bread Sponge; our attention is at once excited by seeing a strong movement in the water, through which tiny atoms are hurried along in swift currents. We fix our gaze on one of the hillocks:-lo! it is a volcano indeed! From the perforate summit of the cone, as from an active crater, is vomited forth a strong and continuous stream of water, and crowds of atoms come pouring forth, disgorged in succession from the interior, and projected far away into the free water, to be followed by unintermitting crowds of others. This is highly curious, and we wonder what is the nature of the power which so strongly conveys to us the idea of an active vitality in a mass so inert and apparently lifeless as this yellow encrusting sponge.

Using his typically vivid powers of description, Henry asks a good question and the power with which sponges generate currents can be seen in a series of videos on the Digital Atlas of Ancient Life web site [4]. He goes on to provide us with the explanation:

The thoughtful observer, watching the evolution of this unintermitted current, ever pouring out with such power and velocity and volume, would ask, What is the nature of the force that vomits forth the fluid? what its seat? and whence the supply? No visible current passes inward from without; still, as the stream is continuous, and yet the quantity of water in the cell does not increase, it is manifest that the water from without must enter in the very same ratio as it is expelled. In order to understand this, we must cut or tear a Sponge to pieces. We shall find that the round apertures are the mouths of a few large canals which run through the interior; that into these open, at irregular intervals, other subordinate canals; that these receive others smaller still; these, again, others, in an ever-diminishing ratio; till at last we can no longer trace them as canals, the whole superficial portion of the Sponge being pierced with microscopically minute and innumerable pores. Into these the external water is constantly being absorbed, carrying with it both oxygen for respiration, and organic matter for nutrition. The influent water, parting with these elements, and thus revivifying the living gelatinous flesh that clothes every fibre, gradually permeates the whole interior, flowing along the pipes in succession, till at length it gathers into the larger canals and is poured out at their apertures..

The chapter in Land and Sea [2] continues with a description of the structure of sponges and the means by which the powerful currents highlighted in the section above are produced:

A Sponge is composed of a clear granular jelly, investing a fibrous or spicular skeleton, formed of horny matter, or flint, or lime. The Sponge which we use for washing has a skeleton made up of fibres of horn, but those which I have been describing have their solid parts made up of flint, the particles of which are arranged in needles (spicula) of a perfectly transparent, solid, brittle glass..

..These spicula or needles, however, that make up the firm portion of the Sponge, are worthy of a little notice. Without them the creature would be a mere drop of glaire, having neither form nor consistence. And yet a heap of needles seems to have little power of assuming or of keeping any definite corporate form, when we remember that they have no adhesion to each other, and nothing, in fact, to keep them together but their mutual interlacement, and the thin glaire by which they are invested..

..The gelatinous flesh has the power of secreting the flint from the sea-water, and of depositing it in regular needle-like forms, and in such an arrangement as to produce the canals and apertures that I have described above. The flesh itself is furnished, on the surface that lines the canals, with curious filaments or hairs called cilia, which are endowed with the faculty of waving to and fro in given directions at the will of the animal (for, strange as it may sound to some of my readers, a Sponge is, beyond all controversy, an animal), and in rhythm or harmony with one another; and these regular wavings impart movement to the water, and cause currents to flow in a given direction though the canals.

These paragraphs show Henry Gosse’s powers of observation, his acquired knowledge, and his wonderful descriptive prose. To some readers, especially those attuned to some of the excellent presentations on the Web [4], it must seem a bit hard-going, for we do not depend on reading in the same way that natural historians did in previous centuries – Gosse marking a transition in that his books use numerous illustrations, many of which he produced himself. Of course, he could not employ moving images.

That sponges are successful is demonstrated by their almost unchanged appearance from more that 500 million years ago and it can be argued that this success resulted from the earlier evolution of cilia and the evolution of the ability to secrete spicules using a number of materials. Of course, Henry Gosse, as a profound Creationist, would have been aghast at the mention of evolution in this context and, although Henry and myself have a shared sense of wonder in looking at the natural world, one of us has a theistic explanation for what we see and the other not.

Sponges are amazing, yet we pay them little attention. Gosse encouraged us to do that and those of us who enjoy shores, and the life they contain, are indebted to him for his encouragement. Using Gosse’s term, it’s good to be a “thoughtful observer” and I wonder if our sense of enquiry about Nature is as high now as it was 150 years ago? Are we losing the child-like gift of curiosity?

[1] https://www.marlin.ac.uk/species/rank/558/Porifera

[2] Philip Henry Gosse (1865) Land and Sea. London, James Nesbit & Co. N.B. This book was a collection of earlier essays and “An Hour among the Torbay Sponges” was probably first published in 1859 according to Freeman and Wertheimer (1980) Philip Henry Gosse: A Bibliography. It was a time when Henry Gosse was at his most outward going and expansive.

[3] Roger S Wotton (2020) Walking with Gosse. e-book.

[4] https://www.digitalatlasofancientlife.org/learn/porifera/