Pearl mussel

Araujo R, Ramos MA (2000) Status and conservation of the giant European freshwater pearl mussel Margaritifera auricularia (Spengler, 1793) (Bivalvia Unionoidea). Biol Conserv 96 233-239... 

Lopez MA, Altaba CR, Rouault T, Gisbert E (2007) The European sturgeon Acipenser sturio is a suitable host for the glochidia of the freshwater pearl mussel Margaritifera auricularia. J Molluscan Stud 73 207-209... 

The Biwa pearl mussel, Hyriopsis schlegelii, is probably the most famous of the freshwater mussels. It was native to Lake Biwa in Japan, though the stocks are now very depleted. It was used in the production of Biwa pearls, which were the first freshwater, non-nucleated cultured pearls to come on the market. They were of an irregular oval shape. 

The cockscomb pearl mussel, Cristaria plicata, lives in Japan and China. It produced the original rice-krispie pearls. They were small, irregular in shape, and had a wrinkled appearance. They were naturally white, but were frequently dyed. The mussels have thin shells and, when pearl cultivation was first attempted in China, were proved to be incapable of producing freshwater cultured pearls of high enough quality. 

The triangleshell pearl mussel, Hyriopsis cumingii, is the oyster now used in China to produce their freshwater cultured pearls, which are of a vastly superior quality to their original rice-krispies . The triangleshell is also farmed in Japan. It has a much thicker shell than the cockscomb, and it can produce nearly perfect round pearls with a good lustre. The naturally coloured nacre occurs in whites, orange-browns and blue-greys. White is the most popular colour (Fig. 9.5). 

The pearl mussels of the eastern United States have also suffered from overfishing, and some species are in danger of vanishing altogether. Most are now protected, but are still endangered by river management works and by pollution. 

Natural pearls from the South Seas were Grst imported to Europe in 1845, and in 1881 the huge silver-lipped oysters were discovered in the seas around north-west Australia. In about 1900 the American ftesh-water pearl mussel industry started up. It was concentrated around the Mississippi, and b an with harvesting mother-of-pearl, most of which went to the button industry. 

Schone, B.R., Dunca, H., Mutvei, H. Norlund, U. (2004) A 217-year record of summer air temperature reconstructed from freshwater pearl mussels (M. margarifitera, Sweden). Quaternary Science Reviews 23, 1803-1816. 

BAi, z., YIN, Y., HU, s., WANG, G., ZHANG, X. LI, j. 2009. Identification of genes involved in immune response, microsatellite, and SNP markers from expressed sequence tags generated from hemocytes of freshwater pearl mussel (Hyriopsis cumingii). Mar Biotechnol (NY), 11(4) 520-530. 

Pearl River Estuary Jade mussel 1996 13 9.5-191 WW Fang et al. (2001)... 

Fang, Z.Q., Cheung, R.Y.H., et al., 2001. Concentrations and distribution of organochlorine pesticides and PCBs in green lipped mussels, Perna viridis collected from the Pearl River estuarine zone. Acta Sci. Circumstan. (Chinese) 21, 113-116. 

Natural or oriental pearls are produced naturally by bivalves, such as oysters and clams, and by a few gastropods, such as abalone. Cultured pearls are induced by the introduction of foreign objects into the mantle cavity. Modem cultured pearls are usually seeded with a sphere made from the shell of Mississippi River mussels (family Unionidae). The culturing process involves prying open the shell and inserting both the seed or nucleus that will become the core of the new pearl, and a piece of donated mande tissue from another oyster. 

Special effect pigments, which can be natural or synthetic, show outstanding qualities of luster, brilliance and iridescent color effects based upon optically thin layers [5.122-5.125]. This visual impression develops by reflection and scattering of light on thin multiple layers. In nature this is not limited to pearls and mussel shells alone there are a multitude of birds, fish, precious stones and minerals, even insects, that... 

It is also possible to divide the groups into marine and freshwater pearls. The molluscs that produce these two types of pearls are termed marine pearl oysters and freshwater mussels. 

There are many natural and cultured pearls of interesting shapes that come onto the market. The freshwater mussels of the eastern United States produce natural pearls that are usually silvery ute> often have a slighdy silky sheen rather than a pearly lustre and can be an amazing variety of shapes (Fig. 9.7). 

Many years after the original pearl cultivation was started, it was realised that it was not necessary to insert a hard nucleus into an oyster to induce it to produce a pearl, and that it was sufficient simply to insert a piece of mantle. This is the method favoured by the Chinese, and gives non-nucleated cultured pearls . The pearls are grown in freshwater mussels, suspended from floats in lakes and rivers. Up to 30 mantle grafts are inserted into a single host mussel s mantle tissue, just inside the shell. 

With all types of cultured pearl, the host oysters and mussels must be tended during the cultivating process. They are regularly lifted from the water and cleaned to remove algae and barnacles that may have accumulated. When the appropriate time has passed for the pearls to have reached their optimum quality, they are harvested. The oysters or mussels are opened and the pearls are extracted. 

Marine pearl oysters that are umed ate all nudeated with a bead and a piece of mantle tissue. Freshwater mussels that ate farmed are implanted with mantle tissue grafts only. In some areas the oysters and mussels to be used are bred and cultivated until they reach maturity and can be implanted. In other areas oysters are cau t in the wild to be cultivated. 

The famous Biwa cultured pearls, named after the lake where they were farmed in Japan, were almost completely exterminated in the 1970s and 1980s. This was caused by a combination of factors, which included pollution from agricultural waste, overfishing, and a freshwater form of red tide. It is taking years to restock the lake with the mussels needed to produce these pearls. 

Natural black cultured pearls were successfully produced in French Polynesia in the 1970s. These types of pearls are expensive to produce as, for example in Australia, the process involves scuba divers with boats equipped as laboratories, to tend to the oysters that are kept off-shore. By comparison, the Chinese fireshwater mussels lie in shallow streams and lakes where it is possible to wade out to them, and the floats holding their cages are often made of empty plastic drinks botdes. The value of a single Chinese pearl today is a r cry fix>m the value of one particularly special pearl in Roman times, which, it is said, paid ft)r a whole battle. 

Some shells have a porcellaneous inner layer, while others produce a nacreous layer. The nacreous effect is called mother-of-pearl and is caused by tiny, overlapping platelets of calcium carbonate in the form of aragonite, which disperse the light to give a play-of-colour. The platelets are polygonal and lie horizontal to the surface. In gastropods and nautilus they are stacked like coins, but they can also be alternated, like a brick wall, as is the case in most bivalves. There can be more than one nacreous layer, as in, for example, freshwater mussels. 

Some of the freshwater mussels that produce pearls also display attractive shells. The cultured pearl industry is very dependent upon beads made from freshwater mussel shells (Fig. 9.10), notably the washboard and pigtoe mussels, which are used for nuclei for cultured pearls. 

The shells of certain eshwaier mussels are used as the nucleus in marine cultured pearls (Fig. 9.10). 

Pure white mother-of-pearl buttons, made from freshwater mussels, may have to be viewed under a microscope to see the aragonite platelets. Lack of these indicates a plastic imitation. 

As with SO many animals the conservation status of the various species changes from year to year. Nautilus has been thought to be endangered but is still widely sold, while some of the freshwater mussels, from which mother-of-pearl nuclei are made for the cultured pearl industry, are in real danger of extinction and are now protected. 

At one time the mother-of-pearl button industry was huge indeed it was so big that it almost wiped out entire populations of freshwater mussels in North America. The industry was in turn almost kUled off by the advent of plastics. Today some buttons are still produced in the Far East and are made mostly from trochus shell. A few more exotic - and expensive - examples from other shells are also manufactured. 

Calcium phosphates are also prepared from natural marine structures such as corals (Roy and Linnehan, 1974 Vago et al., 2002 Papacharalambous and Anastasoff, 1993), mussel (Macha et al., 2013), sea shells (Bahar et al., 2003), sea urchin (Vecchio et al, 2007 Samur et al., 2013), land snail shells (Kel et al., 2012), cuttlefish bone (Rocha et al., 2006), and pearl (Shen et al., 2006) to name just a few. HAp powders have commonly been prepared using a variety of techniques such as wet chemical synthesis, hydrothermal conversion, solid-state reaction, and calcination of bone. 

The principal edible shell-fish are mussels, very large limpets, and niacteas. The Fuegians also feed on sea urchins but the Magellan mussel, a very large bivalve, is their staple food for the greater part of the year. These mussels occasionally contain very small pearls. 

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