MORPHOLOGY AND CRUSHING BEHAVIOR OF THE MINUTE CLYPEASTEROID ECHINOCYAMUS PUSILLUS

Clypeasteroid echinoids are known to be potentially well-preserved in the fossil record. The high preservation potential is due to morphological characteristics unique to clypeasteroids including internal support which are structures connecting the oral and aboral test sides, as well as interlocking plates that securely join neighboring plates. Echinocyamus pusillus, a minute clypeasteroid featuring prominent internal buttresses and solid stereom interlocks, was examined using Scanning Electron Microscopy and X-Ray Micro-Computed Tomography to investigate the microstructure of plate connections and internal supports as well as the importance of organic material for test integrity. A high-speed camera was used to record and explore fracturing behavior and the structural integrity of the test during fragmentation.

Plate interlocking is assured by stereom protrusions with a specific stereom microstructure. Interambulacral buttresses, which extend from the orally located auricles to the outer limits of the aborally positioned petals, and are also joined by stereom interlocking. It is tested if denuded specimens are less robust against physical stress than individuals bearing spines and retaining soft tissues. In addition to structural interpretations, these results can be of importance to the interpretation of the origin of fragmentation patterns as the result of crushing predation or post-mortem transport.