Formation of pearls

by Manisha G

The origin of pearls is still matter of interest and investigation. Although everyone knows that the pearls are formed in oysters, no one is hundred percent sure of what it is that triggers off the formation of pearls. Any shellfish is capable of producing a pearl under suitable conditions. But only those animals which have a shell with a pearly (nacreous) lining can form a lustrous pearl, which is of a gem quality. Pearl forming is the result of the biological process. This process is similar to the formation of the shell, which is of a protective covering of the animal. To understand the nature and formation of the pearl, one should have some knowledge about the anatomy of the animal and structure of the shell.

Various types of pearl bearing oysters:

Haliotis: One of the best-known oysters is the Haliotis, part of the gastropod family. They are found in temperate water as well as tropical waters. The inside part of the shell is covered with grey colored mother-of-pearl and is opalescent. It is spotted with dark layers of horny organic material.

Pinna: Pinna is another type of oysters found mainly in the Mediterranean near the costs of Provence, Italy, Corsica, Sardinia, Greece, and North Africa and at certain points of the Red sea.

Tridacna: Tridacna oysters are also known by the name ‘stoop’ and are found in many tropical regions. Three main varieties of Tridanca are, gigas, squamosal and hipopus maculates.

Strombus Gigas: Strombus gigas, or great conch oysters are common on the coasts of the 400 Bahamas Islands.

The Unionides: Almost all freshwater bivalves belong to the Unionide family of oysters and are more commonly called ‘mussels’ or ‘muletters’. The outside color is usually dark brown and the inside is smooth white mother-of-pearl, sometimes with traces of light brown. They are found in rivers and also lakes in Europe, Russia, China, Japan and America, having a great ability to adapt to local conditions.

The Oyster life and biology:

That pearls are obtained from oysters is a general conception, and indeed, the shell of the pearl oyster resembles strongly that of the true oyster, but the oyster which produces the pearl, so prized in jewelry has more affinity zoologically to the scallop than to the true edible oyster. The pearl oyster belongs to a group of mollusks popularly known as bivalves (animals with a double shell), and the scientific name for the class of these animals is Lamellibranchae.

The life history of the pearl oyster begins with the shedding of the ova or spermatozoa into the sea according to the sex of the animal. Oysters are gregarious animals and therefore the ova or spermatozoa are ejected in localized waters, making the chances of fertilization great. After about 24 hours, the fertilized egg commences to develop a tiny bivalve shell but remains a free floating animal carried about at the whim of the ocean currents. After about a week the animal, if not carried out to places where the sea bed is unsuitable, or if not eaten away by other animals, attaches itself by the thread – like byssus to hard objects or seaweed at the bottom of the sea. These youngsters are at this stage about 0.1 mm in diameter and are termed “spat”.

It is clear then, that the nature of the sea bed has much to do with the formation of colonies of oysters, and suitable conditions of depth and temperature of the water are necessary factors. The dead coral, rocks and shells on the sea bed  to which the oysters attach themselves are collectively known as culch, and artificial culching of the sea bed is sometimes carried out.

The oyster grows rapidly for the first two years of its life and for the first five years has to battle with its enemies – the size of the full grown oysters depend upon its species and upon the conditions in which it lives.

The oyster, like every other animal, possesses a brain, heart, stomach and mouth. It breathes through its gills and feeds itself with micro-organisms, from the sea water.

The longest that an oyster lives is about thirty years. An oysters age can be determined by the grooves in its hinge, just as one tells a tree’s age from the rings in its trunk.

Without oyster or mussels there would be no pearls. The rich or poor harvest of pearls depends upon the oysters.









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