Nature

A Giant Clam Tridacna gigas on Australia's Great Barrier Reef. The mass of pale-blue dots around the edge of the mantle (the blanket-like tissue lapping over the shell's rim) are the creature's eyes (really light-sensing organs).

The shell of a Pearly Nautilus (Nautilus pompilius), a cepalopod, rests on a tropical beach

Cockles and Mussels - but Not Alive-oh!

“WHAT ABOUT SEASHELLS?” SAID OUR EDITOR. “WE HAVEN’T DONE SEASHELLS BEFORE.” MY FIRST REACTION WAS THAT THERE IS QUITE A GOOD REASON FOR THAT

By Mike George

Mike George is our regular contributor on wildlife and the countryside in France. He is a geologist and naturalist, living in the Jurassic area of the Charente

I, personally, have never collected seashells – at least not “modern” ones. I have spent quite a slice of my former existence in looking for fossil seashells, of course, as any geologist will, but not modern ones, with their empty, abandoned look, their endless patterns and shapes, and the sheer impossibility of ever forming a complete collection. A bit like stamp collecting, I guess – which is another form of collecting that doesn’t appeal to me, but that many people find most fulfilling. Then I started remembering, and I remembered a day when I was staying with my beloved Aunt in the Channel Islands, and we went on the day-trip to Herm Island. There is a lovely, curving beach there, entirely made up of seashells, and we spent an idyllic afternoon poking about and studying the lovely forms and intricate patterns of the tiny shells. Remembering that golden day, suddenly I could see the appeal. Also, on my way through the study of Natural History, I have acquired a few books on the subject (a keen naturalist never turns down the offer of a secondhand text-book) so I dug them out and started to re-read them.

What does shell-collecting involve?

For a start, I discovered that there were certain shells that were not included in most shell-collecting textbooks. Apparently, people like to collect shells from the members of the great phylum Mollusca, the second largest phylum after the Arthropoda (insects etc). That covers quite a multitude of forms – everything from gastropods (snails, whelks, winkles etc) and bivalves (oysters, scallops, cockles and clams) to cephalopods (octopuses, squids etc). The sizes of specimens range from 2 metres (the Giant Clam) via the Conches (just under 1 metre) to microscopic. Let’s have a look at these creatures more closely.

These are the ‘headfooted’ creatures, namely squids, octopuses and cuttlefish. Budgerigar owners tend to collect the internal cuttlefish shells, but for a different reason. There is only one cephalopod with an external shell, the Chambered Nautilus, so that would be a fairly limited collecting goal. The shell is the size and roughly the shape of a small melon, and quite unlike anything else. It consists of a spiral of chambers; the animal lives in the largest end-chamber, and the rest of the chambers act as a buoyancy controller. The soft orange markings are uppermost when the shell is alive and swimming, and break up the shell's outline when viewed from above. The bright white living-chamber is underneath, and can hardly be seen against the bright sea-surface above. This is called "countercamouflage". Some think that the Paper Nautilus produces a shell also, but this is in fact an egg-case that is held in two of the creature’s tentacles, and does not act as a “home” for the creature itself. Sadly, the Nautilus, while living for about 20 years, is only sexually mature after 15 years, which cuts down its fecundity. Also, females tend to be outnumbered 2 or 3 to one by males, which again makes them rather sluggish reproducers. Sadly, perfect shells have usually been removed from killed specimens, as shells from owners who have died naturally have a tendency to sustain damage. Many of the sourcecountries now protect the creatures, and the international trade in Nautilus shells is controlled by the CITES regulations. Consequently, they are becoming harder to obtain. I purchased one in a brocante a few years ago for €4; now they are being advertised on-line for upwards of €25 each.

Sometimes also referred to as Pelecypoda or Lamellibranchia, these animals are characterised by having two separate shells (not necessarily the same shape) which work together to enclose the animal, and which it can partially open to enable it to feed, move etc. Usually, the opening edges of the shells fit together to ensure a tight closure. Some bivalves burrow most efficiently. These tend to have a strong, large foot with which the burrow is dug, and which the creature uses to push itself through the substrate. The Razor Shell is a prime example. Others fix themselves to a firm base and stay put. These tend to have a smaller, weaker foot, although some dispense with the foot altogether and attach themselves with stiff threads, known as byssae. The mussel is a good example of this – the byssae are the “threads” that you scrape off when preparing the shells for cooking. Some, such as the Scallop, swim free, using their shells to expel a jet of water to propel themselves. Bivalves are most familiar as food-sources for humans. Scallops, mussels and, of course, the ubiquitous oyster have been a source of human rations for centuries, and by no means as delicacies. Oysters were eaten by the poor as the cheapest source of protein available. Dr Samuel Johnson used to buy oysters to feed his cat, Hodge, and would himself go to the market to buy

We spent an idyllic afternoon poking about and studying the lovely forms and intricate patterns of the tiny shells

A Cone Shell (gastropod), Conus suratensis, probably from the Philippines. Some species of this genus can deliver a poisonous sting when alive

A Triton gastropod shell, possibly Cymatium lotorium, from the Indo-Pacific area, about 10 cm long Sectioned view of a Pearly Nautilus shell Nautilus pompilius (Cephalopod). The animal lived in the big end chamber; the remains of the tube used to control the bouyancy of the other chambers is just visible

A fossil brachiopod (Oleneothyris harlani), about 64 million years old, from New Jersey, USA

It shows the typical shape of a brachiopod, with the aperture for the creature's supporting stem

A living sea urchin, complete with spiny armour. Best not to touch!

An empty shell washed up from a tide today may end up as an empty shell back in the ocean tomorrow where thousands of creatures rely on it for survival

them to avoid embarrassing his servants by sending them to buy such cheap food. Archaeological sites anywhere within reach of the seashore are usually characterised by huge middens of oystershells. Incidentally, it is no use searching your plate of oysters for a pearl. The Edible Oyster does not produce pearls – it is the Pearl-Oyster that does that. Certain other shell-fish also produce items that are classed as pearls – the clam can, as can the conch, which produces a rather charming pink pearl. The bivalves include the largest sea-shell of all, the Giant Clam Tridacna gigas. The heaviest known of these known weighed 263 kg, and many measure over 1 metre in length. Not surprisingly, their method of life consists in staying put, feeding, like all their fellows, on material that floats through their open shells. Legends of men drowning by being trapped by a limb caught in the closing shells are just that –legends. The edges of the shells are, however, sharp and can inflict a nasty wound. Collecting a specimen is generally an engineering feat. (“stomach-footed”) are animals with only one shell, which normally encloses the wholewhile body of the animal. Some have a second hard item called an operculum, with which they can “close” the shell aperture after retreating into it, but this does not constitute a second shell, and is often not even calcified. On the other hand, it should be said that some gastropods have dispensed with a shell completely, or reduced it to an inconspicuous or even internal remnant. On land, we are familiar with the slug. In the sea, the “Nudibranchs” include the sea-slug, sea-hare and others, and some are very beautifully coloured, but the beauty fades after death, or even when they are removed from the water. It is the gastropods that seem to create the most varied and interesting shells. Many are characterised by ridges and projections resulting from the growth-stages of the shell. Some are huge (the Conch and the Triton, for example) but most are small to minute. The range is vast, some are impossibly bizarre in shape, and several are known from a few or perhaps only one specimen.

Are there any other shells to collect?

The text-books didn’t recommend collecting anything else. No brachiopods, which were always the ones that I liked when fossil-hunting. This is probably as well, as the brachiopods, or lamp-shells, once the dominant dwellers in the oceans, are now, thanks to the processes of natural extinction, few and far between and very vulnerable. These creatures look a bit like small Roman oil-lamps. They had two dissimilar shells, the larger with a tiny hole in it where the “stem” on the animal emerged. If you want to collect brachiopods, there are places you can go where you can just pick them up, and these places tend to be inland! My best collecting was done in the Mendips in Somerset, where you can walk across a ploughed field and, when your eye has got used to looking, you can with patience find perfect brachiopods shells just lying in the furrows. Best to wait after ploughing until a few rain-showers have washed the fossils clear of the mud. And don’t forget to check that you aren’t trespassing! There is something called a Chiton, a member of the Mollusca, whose covering is a strange mixture of leathery tissue and small plates of shell, which falls apart after a while and which would be a difficult thing to preserve. The crabs and lobsters are the chief candidates here. The shells of these are in fact the creature’s external skeleton, and therefore tend to fall into a large number of separate units when the flesh is removed. Reconstructing them is a difficult and specialist task, to which as anyone who has wrestled with a crab or lobster in a restaurant can testify. Usually, such creatures are the province of museums who have the time and expertise to do the job. Also in this phylum come the barnacles, with a complex system of interacting shell sections, which do not lend themselves to easy preservation. These are the sea stars, sea cucumbers, sea urchins, sand dollars, and brittle stars, and are again characterised by a complex external skeleton, though in this case, part of the body protrudes through the skeleton in the form of tube-feet, which enable the creature to move. Again, after death the skeleton falls apart in many cases, although the sea urchin has a skeleton of interlocking platelets which can hold together to some extent, especially when small.

Responsible collecting

At this point, I would like to make a plea. If you are going to build up a collection of shells, PLEASE DO IT RESPONSIBLY! By that I mean try not to harm any creature just to add a pretty or interesting shell to your collection. This includes not removing Hermit Crabs from the shells in which they have made their homes. There is no harm in sitting on the sea-shore raking through the shelly debris to find something pretty or unusual, but collecting should be designed to enable one to further one's studies and interests, not just to gain bragging-rights. There is no problem with folks who take home a jar full of dead seashells - there are plenty of those to go around. It's hunting - or paying someone else to hunt - for impossibly rare creatures then slaughtering them so they can say, "I’ve got a whatever-it-may-be in my collection”. That's what I mean. It benefits no-one, not even the collector. Most pocket shell guide books are designed for you to take down to the beach. You can get your book out and have hours of fun trying to put a name to anything you find. Please take only what is already dead;

The heaviest known of leave the living to continue their species. these known weighed 263 kg, and many measure Alternatively, of course, you could always collect stamps! over 1 metre in length

Tutufa bubo - the Giant Frog Snail - a 10 to 30 cm long gastropod, from tropical seas

The aperture of a cowrie shell. Usually tropical to sub-tropical, small specimens of cowries may be found in the Channel Islands on beaches

A Spider-shell (gastropod) of the genus Lambis, from the tropical Indo-Pacific region