Characteristics of the aragonite - calcite transistion in bivalve shells

Abstract

Bivalves and gastropods contain both, calcite and aragonite within their shells (e.g.Checa & Rodriguez-Navarro 2005, Checa et al. 2009). The transition between these phases is neither interlinked nor gradual, it is abrupt and occurs within a spatial range of one to two microns. We have investigated in the shell of the modern oyster Crassosstrea gigas the transition zone between the calcite and the aragonite portion of the shell with TEM (Fig.1) and high-resolution EBSD (Fig. 2). Adult oyster shells are composed mainly of calcite. However, there are small areas within the shell where aragonite is present, shell portions where the muscles (the two adductor muscles, the Quenstedt muscles and the pedal muscles) are attached to the skeleton. Thus, the presence of aragonite at these skeletal parts is required for the overall function of the shell.