Echinoid skeleton: an insight on the species-specific pattern of the Paracentrotus lividus plate and its microstructural variability

Abstract

The skeletal plates of echinoids consist of a peculiar lightweight structure, called stereom, which is organized in a porous three-dimensional lattice-like meshwork. The stereom is characterized by an extremely complex and diverse microarchitecture, largely varying not only from species to species but also among different test plates. It consists of different basic types combined in extremely different ways according to specific functional needs, creating species-specific structural patterns. These patterns can lead to specific mechanical behaviours, which can inspire biomimetic technology and design development. In this framework, the present study aimed to characterize the species-specific pattern of the Paracentrotus lividus interambulacral plate and the main microstructural features regarding its geometrical variability and mechanical responses. The results achieved quantitatively highlighted the differences between the analysed stereom types providing new insights regarding their topological configuration and isotropic and anisotropic behaviour. Interestingly, data also revealed that the galleried stereom present at the tubercle is significantly different from the one located at the suture. These analyses and findings are encouraging and provide a starting point for future research to unravel the wide range of mechanical strategies evolved in the echinoid skeletal structure.

Composite material in the sea urchin Cidaris rugosa : ordered and disordered micrometre-scale bicontinuous geometries

“…Since then, authors have designated the 'rectilinear' stereom type, found in several species of Cidaroids [8], to the Primitive surface [7,12,26]; however a three-dimensional quantitative descriptive of this stereom type is lacking. Recently, a related ordered bicontinuous form, the so-called Diamond surface, was discovered in the ossicles of the starfish Protoreaster nodosus [3] and in the fossilized skeleton of a 385 Myr crinoid Haplocrinites boitardi [12], sparking a renewed interest into the calcite microstructures of echinoderms, including their potential in biomimetics [4,5,27,28].…”

“…Nature's ability to construct specialized composite materials through highly controlled biomineralization processes has inspired many decades of research (reviewed in [1,2]). Echinoderms, such as sea urchins and starfish, have been a focus of much of this research due to their ability to form skeletons with optimized physical properties [3][4][5] and the ease of imaging their optically clear embryos in real time (reviewed in [6]). They form a hierarchical multi-element endoskeleton consisting of stroma and stereom: the stereom consists primarily of magnesiumcalcite, small amounts of stable amorphous calcium carbonate, water and intracrystalline organic molecules; the stroma consists of sclerocytes, collagen fibrils and other extracellular matrix components [7,8].…”