STRUCTURAL MECHANICS OF CLYPEASTEROID ECHINOIDS

Clypeasteroid echinoids are well known from recent environments and the Cenozoic fossil record. Although the multi-plated skeletons of echinoids are generally rapidly disarticulate after the death and decay of an individual, those of clypeasteroids often remain intact during fossilization. In this study, underlying mechanical principles responsible for their high test strength are analyzed in detail.

Denuded tests of Echinocyamus pusillus and Clypeaster rosaceus were examined using scanning electron microscopy and x-ray micro-computed tomography. The samples were analyzed at different hierarchical levels and interpreted with respect to their integrative structural behavior. Results show that numerous resilient structures are present: at the highest hierarchical level, four internal different support types where identified, which correlate with the flatness of the test. Individual plates of the test are interlocked at two levels, where multi-directional sutural interlocking mesh the plates into a mosaic pattern. On a lower hierarchical level, the trabeculae, which are designed to counter multi-directional loads, reach from one plate to another. These trabecular interlocks also vary among clypeasteroid taxa. The clypeasteroids’ skeleton is hence considered a model organism for structurally performative shell constructions.