Echinoderm Calcite: A Mechanical Analysis From Larval Spicules

The flexural stiffness (EI) was measured for simple and fenestrated spicules in echinoid larvae. A Young's modulus (E) of 36.3 x 109 N/m2 was estimated for these calcitic spicules by EI/I where I was calculated independently from measurements made by SEM. The flexural stiffness of fenestrated spicules is approximately three times greater than that of simple spicules. This increased flexural stiffness is due to structural and not material differences between the spicules. At the material level, this calcitic tissue behaves like a composite which will reduce stiffness but increase strength compared to inorganic calcite. At the structural level its porous nature increases its stiffness and buckling strength over that of a solid structure of similar weight. These characteristics should also increase the tensile strength of this skeletal component and increase its usefulness as a strong, stiff element in most echinoderm skeletons.