Structure of the molluscan bivalve hinge ligament, a unique calcified elastic tissue

Abstract

The microstructure of a calcified molluscan bivalve hinge ligament has been studied. Similar to bivalve shell and vertebrate dental enamel, the ligament is composed of oriented crystal bundles or prisms. Electron micrographs of Spisula solidissima ligament show two types of prisms. The lateral surfaces of the ligament are composed of long cylindrical prisms oriented perpendicular to the growing margin of the ligament. The prism crystals are oriented parallel to the prism long axis. In shape and orientation these prisms are similar to those of dental enamel. The prisms observed in the central region of the ligament are cylindrical but constricted at regular intervals, giving the appearance of three-dimensional standing waves. The crystal spacings within these prisms vary regularly along the prism axis. This structure probably responds to compression like an elliptical spring and accounts for the elastic properties of the ligament.