Bivalves are sought after and cultivated for their pearls. Pearls are said to be the queen of gems, because they were discovered over 4,000 years ago and were used as important symbols in many ancient cultures. In spite of their high price, pearls start out as a nuisance for the animal that creates them, which could be an oyster, a clam, or a mussel. Oysters produce the most valuable pearls, which are noted for their luster.
Occasionally grains of sand or parasites accidentally become lodged in an oyster's body and cannot escape. To relieve the annoyance, the oyster begins a defensive action and secretes a smooth, hard, crystalline substance called nacre around the object. Cultured pearls are formed from particles that are intentionally inserted into an oyster.
Introduction of foreign body
Composed of two pieces or valves
INNER SURFACE — OF THE SHELL
Sensory tentacles enable the oyster to detect light and darkness.
Pearl cultivation began in Japan. It consists of inserting into the body of a live oyster a small, round particle made from the shell of a freshwater bivalve. The oyster secretes mother-of-pearl substances from a gland in its liver to cover the object, and the pearl begins to grow.
n The oyster secretes nacre to cover it.
New, uniform layers are constantly added to the pearl, and the cultivator leaves the pearl in place until it reaches the required diameter and quality. During the process, humans intervene only to provide the oysters in farms with the right temperature, water currents, and cleanliness to favor the growth of pearls.
3 to 8 years
TIME IT TAKES FOR A PEARL TO GROW
LAYERS OF NACRE ON THE PEARL
LAYERS OF NACRE ON THE SHELL
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These oysters are suspended from bamboo rafts in areas with J/ti^v abundant plankton.
They can be round or elongated like a grain of rice.
NATURAL CULTURED PEARL PEARLS
surrounds the mantle and controls the flow of water.
The number of pearl cultivators is estimated at nearly 5,000. Japan is the main producer.
joins the two valves at their upper part.
Surrounded -" by nacre
absorb oxygen from the water.
Seldom used; the
have sensory organs.
Cultured pearls make up 95 percent of the pearls currently sold. About 500 million pearls are produced every year. However, pearl farming is a demanding and difficult business because of the nature of pearl oysters: out of 100 oysters cultivated, only 30 will be harvested.
A fiber keeps the shell closed.
OF THE HARVEST WILL YIELD PERFECT PEARLS.
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