Nacreous layers

Perl-mutterpapier, n, naereous paper, -rohr, n, -rohre, /. bead tube (tube filled with glass beads), -sago, m. pearl sago, -salz, n. micro-eosmic salt, -samen, m. seed pearl, -schicht, /. nacreous layer, -schnur, /. string of beads or pearls row of droplets, -seide, /. embroidery silk ardassine, -spat, m, pearl spar (pearly dolomite), -stein, m, perlite adu-laria. -sucht, /. bovine tubereulosis. -weisa, n. pearl white. 

In the formation of pearls and the nacreous layer in shells, an organic sheet is formed 0.2 —0.3p.m away from and between the surfaces of the substrate pearl... 

Figure 14.2. Structures forming the shells ofbivalves [6]. Parts (a)-(d) indicate how the nacreous layer of pearl is formed. A =platy aragonite crystals 0 = organic sheet ...

Figure 14.4. Formation of nacreous layer [6] in (a) a bivalve (b) a snail.

Mutvei, H. On the micro-and ultrastructure of the conchiolin in the nacreous layer of some recent and fossil molluscs. Acta Univer. Stockholmiensis, Stockholm Contr. Geol. 20, 1 (1969)... 

Mutvei, H. Ultrastructural relationships between the prismatic and nacreous layers in Nautilus (Cephalopoda). Biomineralisation 4, 81 (1972)... 

Mutvei, H. Ultra structure of the mineral and organic components of molluscan nacreous layers, Biomineralisation 2, 48 (1970)... 

Hotta, S. Infra-red spectra and conformation of protein constituing the nacreous layer of molluscan shell. Earth Sci. Tokyo 23, 133 (1969)... 

Isoenzymes III and VII have a more specialized distribution. Carbonic anhydrase III is abundant in adipocytes which use bicarbonate in fatty acid synthesis.7 Isoenzyme V is present in the mitochondrial matrix and is also abundant in both adipocytes and liver.7 8 Isoenzyme IV is a larger membrane-associated form, while VI is secreted into the saliva.10 Carbonic anhydrase has also been identified in E. coli.,11 in a methanobacterium,12 and in green plants.13 133 A 60-kDa carbonic anhydrase called nacrein is found in the organic matrix of the nacreous layer of the pearl oyster, the layer that forms aragonite (orthorhombic calcium carbonate) in the shell and in pearls.14... 

Fig. 27. Space-filling model of the B chain of insulin. Numbers indicate position of carboxyl oxygens (after Warner231)). The MM in nacreous layer of molluscs is assumed to be built according to the same principles...

A particularly well-studied structure is that of the nacreous layer (= Mother-of-Pearl) of molluscs, which will be used below to illustrate our concepts17 34,46,233-241). 

Also, increase in water temperature favors -conformation. Inasmuch as the conformation of CP probably determines the tertiary structure of MM, slight changes in CP conformation introduced by cellular or environmental effects may alter MM conformation. This in turn is reflected in the mineral form and structural pattern of the inorganic phases. Perhaps, nacreous layers in molluscs represent an almost ideal situation where MM and CP are aligned in a symmetrical way. In fish otoliths, the fibrous organic matrix is a mixture of helices and 0-pleated sheets. It is tentatively concluded that the morphology of shell structures is a macroscopic expression of the molecular interactions between MM and CP which are controlled in part by cellular activities and in part by the environment. 

Bevelander, G., and Nakahara, H. An electron microscope study of the formation of the nacreous layer in the shell of certain bivalve molluscs. Calc. Tiss. Res. 3, 84-92 (1969). 

Shell brooch is made from the shiny inner nacreous layer of shell. The layered texture of the nacre is clearly visible. 

Shell cameo designs are usually carved from the white porcelain shell layer against a background of the darker nacreous layer underneath. 

Shell has been cut into a huge variety of forms that are intended to be used with the shiny nacre uppermost. Sometimes the nacre is used alone, but some of the porcelain layer is often retained to give an object strength. Mother of Pearl is the name given to objects that are made from the nacreous layer of shell, whether it includes the porcelain or not (Figure 5.7). 

Shells, pearls, and other invertebrates may be found in art and anthropology collections as worked objects, or as part of composite objects. The nacreous layer of mollusk shells is commonly referred to as Mother-of-Pearl, and may be found as inlay in objects made of wood and stone, and as small decorative and utilitarian objects such as buttons, jewelry, tool handles, and small carvings. Pearls are used most often in jewelry, drilled through so that they can be strung like beads. They are also used as decoration on fabric and objects d art. 

Nacre nacreous layer or mother-of-pearl the inner shell layer in some mollusks... 

Transmission electron microscope studies have shown that the organic interlamellar membranes have a lamellar structure (Figure 16(a), (b)). This structure varies according to the taxa. Some fenestrations or holes have been described, and they have been considered to favor the passage of fluid substances needed for the minerahzing process. The decalcificafion process of the nacreous layer, and later all the mollusc layers and invertebrate tests, has shown... 

Figure 16 Successive models of the nacreous layer of mollusk shells...

H. Mutvei, The Nacreous Layer in MoIIuscan Shells, in The Mechanisms of Biomineralization in Animals and Plants , eds. M. OmoriandN. Watabe, Tokai University Press, Tokyo, 1980, p. 49. 

South Sea pearls are large, and are grown in, for example, the silver-and golden-lipped oysters, which are much larger than the Akoyas. South Sea pearls are also nucleated with mother-of-pearl beads, but only one is inserted at a time. They produce nacre faster than Akoyas and are left in the sea for two years, resulting in the thicker nacreous layer that is typical of South Sea pearls (Fig. 9.4). The oysters are suspended from off-shore floats, at a depth of 10 to 15 metres, and are tended and harvested by divers who sail out to the oyster beds on boats equipped as laboratories. 

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. 

The molluscs from New Zealand are known as paua, while their cousins across the Pacific on the American coastline are known as abalone. Both occur in glorious iridescent greens, blues, pinks and purples. The nacreous layer has a surface pattern resembling waves, which is caused by concentiatioiis of organic matrix. In the centre is a more uneven area where the animal was attached to the shell. The... 

The shell is partitioned into connecting chambers, with the mollusc occupying only the last one. The rest are filled with gas to give buoyancy. The inner layer of the shell is nacreous, and, as with paua shells, the periostracum can be polished away to reveal the nacreous layer beneath (Fig. 10.9). The material is most commonly used as mother-of-pearl inlay. 

Fig. 4.10. Schematic representation of the structural relationships between protein sheets, aragonite crystals, and chitin fibres in the nacreous layer of N. repertus ...

---