Zoology or Animal Biology
Clams Oysters and Scallops

How does an oyster make a pearl?

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2010-06-06 11:31:35

Natural pearls

Contrary to popular belief, a natural pearls is not

formed by a grain of sand. This story is an urban legend.

A natural pearl forms inside a bivalve mollusk when the shell

has been invaded by a parasite or damaged. The most common reason a

natural pearl will develop is due to parasitic invasion.

The parasite wil burrow through the periostracum layer (outer

layer) of a mollusk shell and into the mother-of-pearl beneath.

When the parasite penetrates the mother of pearl in comes in

contact with the mollusk's mantle muscle. This muscle contains

cells known as epithelial cells. These cells produce a substance

called nacre which coats the inside of the shell (mother-of-pearl)

and is the substance of which a pearl is composed.

The parasite becomes lodged in this mantle muscle and dies. The

mollusk's definsive reaction is to grow a sac around the intruder.

This sac is called the pearl sac. Once the sac encases the intruder

the cells begin to deposit nacre- which is composed of aragonite

and calcite (a calcium carbonate compound) platelets.

Cultured Pearls

Cultured (marine) pearls are grown by inserting a rounded bead

of mother-of-pearl and a piece of mantle tissue containing

epithelial cells from a donor mollusk into the gonad, or

reproductive organ, of a host mollusk. The donor tissue grows into

a pearl sac around the bead. As in natural pearl production, this

sac then deposits nacre.

Maturity time of artificial oyester pearl

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