Pearl formation in mollusca for BSc I students

Pearl formation in mollusca for BSc I students

1. Pearl formation in molluscaPearl formation in mollusca

2. PEARLSPEARLS
Pearls are highly esteemed biological gems
having smooth, lustrous and variously
coloured deposits (nacre) around a grain of
sand or other foreign particles in the shells of
certain marine oysters and freshwater
mussels.
Composition of nacreous deposit:
82 - 86% - Calcium carbonate (aragonite crystals)
2-4% - water
10-14% - Conchiolin, which impart shining to the pearls

4. Classification of PearlClassification of Pearl
Natural Pearl: Natural pearl is formed when a foreign
particle viz., piece of sand, animalcule, small parasite, algae
etc. enters the body of certain oysters/ or mussels by chance,
and is not rejected out easily. Oysters or mussels start
depositing a shiny coating on the particles layer by layer that
ultimately results in formation of pearls.
Cultured Pearl: The cultured pearls are produced by
inducing oysters to deposit nacre around a surgically
implanted foreign body of a particular shape and size into
some identified locations.
Artificial Pearl: The artificial pearls are made of plastics,
marbles, glass, talc, ivory or shell beads etc. They are painted
with pearl essence, which is a mixture of enamel and silvery
extract of fish scales (iridescent guanine -C
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5. Facts
Kokichi Mikimoto : Father of Cultured Pearl
Tokichi Nishikawa (1907) gave the “pearl sac
theory”.
This theory state that the pearl secreting cells
of the mantle migrate into the body of the
oyster under the stimulus of a foreign particle
and by series of cell division form a pearl-sac
around the foreign body. The pearl-sac in turn
secretes the nacre, which is deposited over
the foreign body forming a ‘natural pearl’ in
course of time.

7. TAXONOMY and DISTRIBUTION TAXONOMY and DISTRIBUTION
of OYSTER and MUSSELof OYSTER and MUSSEL
Oyster (Marine)Mussel (Freshwater)
Phylum: Mollusca
Class : Bivalvia

8. Fresh water mussles in pearl Fresh water mussles in pearl
formation in India.formation in India.
pearl formation to the desired size,
shape, colour and lusture. In India, three
species of commonly available freshwater
mussels viz., Lammelidens marginalis,
L. corrianus and Parreysia corrugata can
be used to produce good quality pearls.

9. Pinctada maxima
P. fucata
P. margaritifera
The species of pearl oysters found in India
comes under genus Pinctada, which Includes
most of the pearls found in fashion.
Pinctada maxima
South Sea pearls
Pinctada fucata
Akoya pearls (classic)
Pinctada margartifera
Tahitian peals (black)

12. BIOLOGYBIOLOGY
•Pinctada fucata - commonly used for pearl production
•attaches to hard substratum by means of byssus threads
•Stenohaline ; survives short term salinity fluctuations
•Filter feeder, mainly on phytoplankton, occasionally on bivalve eggs and copepods
•Life span - 5-6 years, maximum size 10cm
•Annual growth rate - 50mm
•Environmental factors such as depth, transparency, temperature, salinity, currents,
calcium content of water, food and foulers influence growth rates
•Sexes are separate hermaphroditism and change of sexes from one spawning season to
another are not uncommon
•Attains maturity at a size of 25-30mm
•Two peak spawning seasons- 1.during July to August; 2. from November to December
•Eggs and sperms are shed in water, fertilization is external
•Hatching takes place in about 4 hours
•Spat settle when 0.3mm in size
•Spat availability in the wild fluctuates, hence hatchery produced spat are used for
culture.

14. FORMATION OF NATURAL FORMATION OF NATURAL
PEARLPEARL
Pearl is formed due to secre
­tion of the
mantle tissue. The nacreous layer of the pearl
is secreted by the outer epithelial layer of the
mantle. This layer has the capability to
rearrange and regenerate itself and remain
viable when disturbed and also when
transplanted in other tissues of the animal.
The inner epithelium and the connective
tissue, on the other hand, would disintegrate
when transplanted.