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THE PEARL OYSTER
Anatomy of an Oyster
Oysters are highly sensitve and quite complex creatures. The oyster like every other animal,
possesses a heart, stomach, and mouth. It breathes through its gills and is able to move using its
'foot.'
General Characteristics
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. The most interesting aspect of the oyster is the mantle. It is a fold of epithelial
material that envelopes the animal and the halves of the mantle are joined together at the hinge. The
outer edge is split into two parts: one covers the edge and crust of the shell and the other covers the
mother of pearl which it produces through its epithelial cells. All pearls whether natural or cultured
depend on this part of the mantle, so it is vital to be able to tell them apart so as to understand the
process of pearl secretion.
Location and predators
Oysters are located at contrasting depths from very shallow waters to the edge of a Continental
Shelf in 80 metres of water. Oysters survive best on a gravel or sandy bottom and prefer an open
aspect, although some can be found in reefs. Enemies include octopus' and stingrays, and cyclones
are known to cause a great deal of mortality as well as unseasonal changes in weather to which
they are very sensitive.
Reproduction
Th oyster has the ability to change sex from male to female.When an oyster starts to breed it sets
off a chain reaction with neighbouriong oysters. Eggs and semen unite at the mercy of the currents
and the fertilised eggs remain in a plankton state for 20 to 30 days. By the 45th day, the oyster
reaches a diameter of 10mm.
Oyster Habitat and Food
The oyster requires a flowing current to bring organic detritus to them, on which they feed, and is
filtered through their system. Any other fragments such as sand and coral which come their way as
they feed on the currents, are naturally filtered away, and generally do not pose a problem. It was
thought that an irritating piece of grit was the basis of natural pearls, however the irritant is now
believed to be a tiny marine worm or boring creature. When an oyster finds a suitable place to live,
an organ situated in the foot secretes a fibrous matrerial, the byssus, which holds it in place to its
location. The oysters attach themselves to suitable anchor points at depths of 15 to 20 metres and it
is apparent that the light plays a major factor while deciding where to stay.
