The mineralized shell (consisting of calcium carbonate) of the tropical freshwater snail Biomphalaria glabrata was investigated with high resolution synchrotron X-ray powder diffractometry and X-ray absorption spectroscopy (EXAFS). Parts from different locations of the snail shell were taken from animals of different age grown under various keeping conditions. Additionally, eggs with ages of 60, 72, 120, and 140 hours were examined. Traces of aragonite were found as first crystalline phase in 120 h old eggs, however, Ca K-edge EXAFS indicated the presence of aragonitic structures already in the X-ray amorphous sample of 72 h age. The main component of the shell of adult animals was aragonite in all cases, but in some cases minor amounts of vaterite (below 1.5%) are formed. The content of vaterite is generally low in the oldest part of the shell (the center) and increases towards the mineralizing zone (the shell margin). In juvenile snails, almost no vaterite was detectable in any part of the shell.

No abstract

No abstract

The cover picture shows the sweet-water snail Biomphalaria glabrata. Its shell consists of calcium carbonate in the aragonite modification (see the packing plot, upper left). The composition of the shell in embroynic and adults snails was studied with high-end solid state chemical methods, that is synchrotron powder diffractometry (EXAFS, upper right). The delicate structure of the shell and the extraordinary hardness compared with ªsimpleº calcium carbonate is due to the biological control of the crystallization process. If calcium carbonate is crystallized in the laboratory, usually the calcite modification (lower right) is obtained. This work is described in more detail by M. Epple et al. on p. 3679 ff.

No abstract