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large freshwater mussels pearls 3 8 mm ans 18 ans 4

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Unformatted text preview: oyster of Tahiti (“black pearls” up to 13 mm) • Hyriopsis sp. - large freshwater mussels (pearls 3 – 8 mm) ANS 18 ANS 4 Distribution of marine pearl species ANS 18 ANS 5 Marine pearl biology • All of the pearl oyster species grow best at subtidal depths; 10 - 80 m and have a strong preference for hard substrates. Salinity optima is fairly narrow, 27 - 34 ppt. and these species do best in pollution-free waters in areas with strong currents. Temperature preference for Pinctada maxima and P. margaritifera is about the same, 19 32oC while P. fucata has a lower range, 10 25oC. Colder temperatures reduce growth and nacre deposition as well as making them more susceptible to disease. ANS 18 ANS • 6 Pearls Natural pearls are formed when epithelial cells, which secrete a coating of thin concentric layers of mother-of-pearl material called “nacre”, surround an “irritant” in the mantle of a mollusk. Often the complex will be attached to the shell on one side producing half round pearls called “mabes” (mah-bays). The nacre is a combination of calcium carbonate in a crystal...
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