Shells and molluscs

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The next time you visit the beach, look out for shells, collect them and study them. They have many uses and many interesting tales to tell.

I’m sure that many of you like to go to the beach. An interesting and popular hobby that many young persons, and grown-ups pursue is shell-collecting. With each sweep of the tide, a huge mass of material comes up the shore, including shells, living things, dead wood, bits of plants, skeletons, bottles and the inevitable pile of rubbish! Looking through all this, or beach-combing as it is popularly called, can be fun!

The scientific study of shells is called conchology. Seashells are actually skeletons. Just as humans have skeletons inside their bodies, called internal skeletons, some animals like molluscs have their skeletons outside their bodies. This external skeleton serves to protect soft-bodied creatures from the strong waves, and from possible predators. The way in which molluscs grow shells is rather similar to the way humans grow nails. A fold of skin, called the mantle, builds up, layer by layer, until all the layers harden to form the shell. All shells are a mixture of horn and chalky crystals that remain intact even after the creature inside it dies. Special muscles hold the inhabitant and its shell together. As the animal grows, the shell grows with it. Shells grow fast if there is plenty of food available, the water is warm and conditions are generally good.

The best time for collecting and studying shells is during low-tide. You need nothing more than a notebook and pencil, spade, tape-measure, bucket, sieve, magnifying glass, net, plastic bags and boxes. If you are only interested in collecting shells, then you’ll find plenty on the strand line or the high-tide mark. But if you want to be more adventurous and study molluscs too, then you must venture down to the low-tide mark and dig deep into the sand. Fill your sieve with sand and then wash the sand away. Chances are that you’ll catch a variety of bivalves (two part shells) at the bottom. Make careful notes – measurements, colour and description. Observe how they dig back into the sand. It’s far easier to locate and study molluscs on rocky shores, because here they cannot dig themselves into the sand. They cling, instead, to crevices and cracks in rocks, or hide under them. When you remove them to inspect them, however, make absolutely sure that you replace them carefully and gently.

You can store empty shells, after washing and drying them, in boxes lined with cotton wool and covered with a thin sheet of plastic. Mark each box with the name of the shell and where you picked it up from. While a majority of the shells found on sandy beaches are bi-valves, rocky beaches abound in gastropods, where the molluscs creep up the rocks feeding on algae and seaweed by scraping them off the rocks with their rough tongues. When the tide goes out, they clamp down on to the rocks to retain and preserve vital body moisture. The molluscs of rocky shores (limpets, etc.) are hardy little creatures that can withstand the beating of the waves against the rocks.

Perhaps the most beautiful shells in the world are found in the warm waters of the Pacific and Indian Ocean, where they grow rapidly. The largest shell, the giant clam, is found here and also one of the rarest of all shells – the white-tooth cowrie. The most expensive shell is also tropical – the Bengal cone – for which a collector paid roughly 1,350 pounds! Shells have always been put to great use, both in days gone by and today. The money cowrie was used as money, as you can guess from its name; shells have been used to make jewellery; the Indian chank shell is blown at religious ceremonies and still others, like the mother-of-pearl, are used to make buttons. And, of course, the oyster is prized for its pearl. Certain bi-valves, like the noble pen shell, fasten themselves on to rocks with the help of special threads called byssus which were used to weave a very fine, silk-like cloth. Some molluscs produce a rich purple dye and, finally, large tropical shells in our country were once used for carrying water and even as babies’ feeding bottles!


bittu-1

Bittu Sahgal

The writer is Editor, Sanctuary magazine

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