engleski

The mineralogy of freshwater snail shells of Belgrandiella fontinalis and Belgrandiella kuesteri (Molusca: Gastropoda: Hydrobiidae

In the last decade a wide scope investigation of the biomineralization process in marine, land and freshwater beings has been undertaken (e.g. D. Medaković, S. Popović, B. Gržeta et al. Marine Biology 101(1989) 205-209, 122 (1995) 479-485, 129 (1997) 615-623, Periodicum Biologorum 101 (1999) 143-149). The present work has been focused to study the mineral composition of shells of snails Belgrandiella fontinalis (F. Schmidt 1847) and Belgrandiella kuesteri (Boeters 1970), collected from three freshwater springs in northeastern Slovenia. It was found by X-ray powder diffraction that the studied shells contained aragonite, calcite, dolomite and quartz. The fractions of minerals in particular shells were determined. X-ray diffraction showed that the analysed gastropod shells consisted of two or more distinct inorganic layers. The outer shell layer for all the species and all sampling localities contained aragonite. The outher layer of B. fontinalis collected at one locality contained also a small fraction of calcite (1 molar%) besides the domonant aragonite. Calcite was indentified in the inner layer(s) of both studied species (2 to 3 molar%), while quartz was found only in B. kuesteri (5 to 7 molar%). However, both species sampled at one of localities showed the presence of dolomite (about 20 molar%) in the inner layer(s). The presence of dolomite in the shells of adult gastropods and even molluscs is unusual. A possible formation mechanism and specific ecological factors which influence the precipitation of dolomite in the shells of different Belgrandiella species are discussed.

XRD; Belgrandiella fontinalis

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