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/

 

 

Looking for Torbay Bonnets

 

I was very lucky to have been born, and brought up, in Torbay on the Devon Riviera coast, only leaving to go to University when I was 18 [1]. Although I now live in Hertfordshire, I enjoy my return visits to South Devon for a couple of days each year, and I’m hoping that 2021 will allow me to re-connect with my roots; COVID-19 having prevented travel in 2020.

Perhaps because I live inland, I have a strong love of coasts and I am drawn, especially, to the red sandy beaches of Torbay and the rocky outcrops of sandstone and limestone that are such features of the Bay and the adjacent coast. Every visit I make includes a walk along a beach and, unlike most people, my fascination is with the strand line of material left by the retreating tide. I started beachcombing nearly seventy years ago, when there was far less plastic and other refuse on the shore, most of that being discarded by ships, or coming through sewage outlets from around the world. My discoveries then were mostly of seaweeds (from which colonising sandhoppers scurried away when the weed was turned over) and the remains of marine animals, with shells and shell fragments being abundant. Sometimes, there was something unusual – a mermaid’s purse or a comb jelly – but mostly the remains were of molluscs, their soft body parts having been decomposed long before. The commonest shells were those of cockles, clams and razor clams and, usually, there were also good numbers of limpets, slipper limpets, winkles (of several species) and top shells. They intrigued me as a child, as I had such little knowledge of the aquatic world, except that acquired by exploring rock pools.

After a storm, the amount of detritus gathered at the strand line could be impressive and the number of shells, and shell fragments, washed up after the “big freeze” of early 1963 made one wonder just what had been left behind in, and on, the substratum of the shallow bay. Although I wasn’t aware of them at the time, among the shells would have been those of “Paignton Cockles” and “Torbay Bonnets”. I have described Paignton Cockles in an earlier blog post [2], but many readers will not have heard about Torbay Bonnets (also known as Fools-cap Limpets). These are extracts from a description written by Gosse in the mid-Nineteenth Century [3]:

The Fools-cap Limpets.. ..have the shell shaped like a somewhat high cone, with the summit a little produced, and turned over backwards. The surface is commonly marked with lines (striæ), and covered with a horny skin, which is sometimes invested with a short velvety down. The interior has no plate or partition of any kind..

..The only British species is commonly known by the appellation Torbay Bonnet; it also bears the names of Fools-cap Limpet, Cap of Liberty, and Hungarian Bonnet, all of which designations.. .. have an obvious reference to its form. It is a rather large shell, being frequently more than an inch and a half in diameter, and an inch in height. Its substance is rather thin, though strong, and somewhat translucent; its colour is a delicate pink, or flesh-white, though this is concealed, especially around the lower part, by an olive-coloured skin, covered with shaggy down. The interior of the shell is delicately smooth, and of the same roseate hue as the exterior.

The animal is usually pale yellow, with a pink mantle bordered with a fine orange-coloured fringe. The head, which is large and swollen, is tinged with brown.

Though generally distributed, The Fools-cap must be considered a rare shell. Torbay, as one of its familiar names indicates, is the locality in which it occurs in greatest abundance.

Gosse provides an illustration of the shell (above upper) that can be compared to a photographic image taken by Georges Jansoone (above lower). In the latter, note that the periostracum is missing, this being the coating of the shell that Gosse refers to. In both images, there is no animal present, just the shells that they secrete, the animals having a superficial resemblance to limpets and slipper limpets, the former being familiar to us.

Although Gosse refers to Torbay Bonnets as Fools-cap Limpets, they are very different to common limpets, although they share features with slipper limpets. Common limpets use a file-like tongue (the radula) to scrape over the surface of rocks to remove algae and biofilm and are mobile when covered by water, returning to their “home scar” should they live on rocks in the inter-tidal. Slipper limpets and Torbay Bonnets, in contrast, are sedentary and feed on tiny particles carried into the cavity of the shell by huge numbers of tiny beating hairs called cilia. The particles are then trapped on mucus and carried to the mouth for ingestion, the radula being important in this process [4].  

I began this post about Torbay Bonnets by describing my love of beachcombing in Torbay before I went off to University. There, I was taught about molluscs by Professor Alastair Graham and Dr Vera Fretter (the latter was my tutor) and they were acknowledged experts on British snails, like limpets, slipper limpets, and Torbay Bonnets. I wish that they were still alive, as I would love to chat to them to find out more about these fascinating molluscs (I didn't have so many questions when I was a student...). Their monograph on snails (see image below) remains a classic of scholarship and research and, just like Gosse, they made all the illustrations themselves. Few of us have these skills, and maybe they are not needed in the age of videography and the internet, but we can still enjoy beachcombing and the excitement of discovery along the strand line. I’m certainly looking forward to visiting South Devon in 2021 and I shall be looking out for Torbay Bonnets.

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

[2] https://rwotton.blogspot.com/2017/11/the-legendary-paignton-cockles-and-some.html

[3] Philip Henry Gosse (1854) Natural history. Mollusca. London, Society for Promoting Christian Knowledge.

[4] C.M.Yonge (1938) Evolution of ciliary feeding in the Prosobranchia, with an account of feeding in Capulus ungaricus. Journal of the Marine Biological Association of the United Kingdom 22: 453-468.

[5] Vera Fretter and Alastair Graham (1962) British Prosobranch Molluscs: their functional anatomy and ecology. London, The Ray Society.