980. AN INQUIRY INTO THE MECHANICS OF TRIGONIID HINGE SYSTEM

Abstract

The gear-like intricate dentition of the Trigoniidae appears to fix the axis of valve opening and closing movement, while the opening and closing forces must be generated independently by the ligament and adductor muscles. As a result of experiments and moment analysis on living specimens of Neotrigonia margaritacea (Lamarck), it was found that the three axes determined by dentition, ligament and adductor muscles are largely different from one another in orientation. Provided that minimum friction is required for the smooth hinge movement, the opening force by ligament and closing force by adductor muscles have to compensate each other, and the axis of their resultant force may coincide with the dentition axis. The relatively short ligament in trigoniids seems to enable such a remote valve movement axis from the postero-dorsal margin as well as the formation of remarkably pennate shells like Pterotrigonia.