X-ray Diffraction Studies of Echinoderm Plates

Abstract

X-ray diffraction studies confirm that, with few exceptions, each skeletal element of echtinoderms is a single crystal of magnesium-rich calcite and that a relation exists between the shape of the element and the crystallographic a- and c-axes. The exceptions incluide the teeth of echinoids, and the calcareous ring as well as the anal teeth of holothurians. The tubercles of an echinoid plate begin their growth as parts of the single crystal of the plate; under the mechanical action of the spines that are attached to them, they become partly polycrystalline, as shown by scanning electron microscopy and by x-ray powder diffraction. The interface between inorganic crystalline and organic amorphous matter in the skeletal element appears to be the first example reported in nature of a periodic mninimal suirface.

Transient precursor amorphous phases in biomineralization.In the footsteps of Heinz A. Lowenstam

“…The possibility of growing the larvae in synchronized cultures greatly facilitates investigating larval development, including the spicule formation processes (for recent comprehensive reviews, see Wilt [31,32]). Surprisingly each spicule behaves optically and crystallographically as a single crystal of calcium carbonate (calcite) [33], despite the fact that morphologically the spicule bears no resemblance to an inorganic single calcite crystal [34][35][36]. This was first observed by light microscopy under polarized light.…”

The classical theory of minimal surfaces

“…This property makes TPMS objects of interest to neighboring sciences, such as material sciences, crystallography, biology and others. For example, the interface between single calcite crystals and amorphous organic matter in the skeletal element in sea urchins is approximately described by the Schwarz Primitive surface [3,50,156]. The piece of a TPMS that lies inside a crystallographic cell of the tiling is called a fundamental domain; see Figure 6.…”

“…They have collaborated since 1998 with common research interests in minimal and constant mean curvature surface theory in three-manifolds. 50 See Footnote 21 for the definition of stability in the non-orientable case.…”

Unipolar assembly of zinc oxide rods manifesting polarity-driven collective luminescence

“…When assembling into larger systems, the constituent crystals orient themselves with respect to each other following certain specific criteria. The macroscopic shape of a skeletal plate of sea urchin is thus dictated by the crystallographic axis of calcite (6). By using peptides extracted from living organisms, oriented assemblies of nanoparticles can be obtained in vitro, too (7).…”

“…Such processes are abundant in natural systems and are of fundamental importance because these constitute the basic building blocks in many inorganic or biomineralization processes (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). When assembling into larger systems, the constituent crystals orient themselves with respect to each other following certain specific criteria.…”