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Sea urchins (ˈɜrtʃɪnz) are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin are distributed on the seabeds of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of sea urchins are round and covered in spines. Most urchin spines range in length from , with outliers such as the black sea urchin possessing spines as long as . Sea urchins move slowly, crawling with tube feet, and also propel themselves with their spines. Although algae are the primary diet, sea urchins also eat slow-moving (sessile) animals. Predators that eat sea urchins include a wide variety of fish, starfish, crabs, marine mammals, and humans. Like all echinoderms, adult sea urchins have fivefold symmetry, but their pluteus larvae feature bilateral (mirror) symmetry, indicating that the sea urchin belongs to the Bilateria group of animal phyla, which also comprises the chordates and the arthropods, the annelids and the

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The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution

Anders Meibom

The sea urchin tooth is a remarkable grinding tool. Even though the tooth is composed almost entirely of calcite, it is used to grind holes into a rocky substrate itself often composed of calcite. Here, we use 3 complementary high-resolution tools to probe aspects of the structure of the grinding tip: X-ray photoelectron emission spectromicroscopy (X-PEEM), X-ray microdiffraction, and NanoSIMS. We confirm that the needles and plates are aligned and show here that even the high Mg polycrystalline matrix constituents are aligned with the other 2 structural elements when imaged at 20-nm resolution. Furthermore, we show that the entire tooth is composed of 2 cooriented polycrystalline blocks that differ in their orientations by only a few degrees. A unique feature of the grinding tip is that the structural elements from each coaligned block interdigitate. This interdigitation may influence the fracture process by creating a corrugated grinding surface. We also show that the overall Mg content of the tooth structural elements increases toward the grinding tip. This probably contributes to the increasing hardness of the tooth from the periphery to the tip. Clearly the formation of the tooth, and the tooth tip in particular, is amazingly well controlled. The improved understanding of these structural features could lead to the design of better mechanical grinding and cutting tools.

2009

Ultrascale and Microscale Growth Dynamics of the Cidaroid Spine of Phyllacanthus imperialis Revealed by Mg-26 Labeling and NanoSIMS Isotopic Imaging

Stéphane Laurent Escrig, Anders Meibom, Jaroslaw Hubert Stolarski

Growth dynamics of the primary spine of the cidaroid sea urchin Phyllacanthus imperialis was assessed for the first time using pulsed Mg-26-labeling and NanoSIMS isotopic imaging. The sea urchin was incubated twice (for 48 h) in artificial seawater with elevated level of Mg-26. After each labeling event, the sea urchin was returned for 72 h to seawater with natural isotopic abundance of Mg-26. NanoSIMS ion microprobe was subsequently used to visualize the labeled regions of the spine with submicrometer lateral resolution. The growth of the new skeleton was restricted to the distal-most and peripheral portions of the spine. Skeletogenesis involved mostly the deposition of continuous thickening layers and lateral growth involving bridges between previously formed trabeculae. The timescale of formation of individual thickening layers (ca. 1 mu m in width) on the stereom trabeculae was on the order of 1 day. Longitudinal growth occurred mainly at the periphery in the form of small portions of the thickening deposits or more massive microspines that appeared to branch and fuse with those above and below. These microspines were found to grow at about 10 mu m/day. These results reveal that the skeletal growth of a juvenile cidaroid spine is complex and highly heterogeneous, with different extension rates depending on the stage of the stereom development and/or direction of the growth fronts. The growth pattern observed here at the submicrometer scale provides direct evidence supporting the earlier suggestions that the lamellar structure of echinoderm stereom is formed by periodic deposition of continuous mineral layers. (C) 2014 Wiley Periodicals, Inc.

Wiley-Blackwell2014

High-Yield Synthesis of Multi-Branched Urchin-Like Gold Nanoparticles

Francesco Stellacci

Here, we report on an aqueous room temperature synthesis method for the production of gold nanoparticles that have a number (> 4) of branches ultimately resembling the shape of sea urchins. The particles are synthesized in the presence of water soluble thiol terminated molecules, used as ligand molecules. These nano-urchins are produced in high yield and exhibit unique optical properties. The thiolated ligands stabilize the particles, making it possible to dry them and store them for days. When redissolved, the particles show some aggregation but not a loss in shape; their extinction spectrum shows a shift in the plasmon resonance from 585 to 622 nm together with a peak broadening. Large local electromagnetic (EM) field enhancements are expected near the sharp featured branches of the nanourchins. Finite difference time-domain (FDTD) calculations performed on a nanoparticle with four branches show enhancements of the light intensity relative to the incident field of approximately 3000-fold. We reason that these particles will find applications as materials for surface enhanced Raman scattering (SERS).

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