ABSTRACT
The primary spines of Diadematidae are very flexible hollow spines. Their bending ability is caused by the material properties of the calcite, and by the anatomy of the spine skeleton. Spines were bent in order to determine the material properties of the spine calcite of Diadematidae. Therefore the diameter of the spines had to be calibrated (fig. 1) and the areas of four cross- sections had to be determined (figs. 2, 3). This data were used to calculate the second moment of area with the help of a digitizer and a special computer-program (Hansmann, 1978).
