Figure 2: The photonic architecture in the shell of the blue-rayed limpet.

(a,b) SEM images after sectioning and polishing along the white line of the limpet shell denoted in the upper left inset (the centre part of the polishing line, marked in red, represents the area of the cross-section shown in (a)). Scale bars, (a) 5 μm, inset 1 mm, (b) 2 μm. The two different structural components—a regular multilayer on top of a disordered array of colloidal particles (marked with the white dashed lines)—are embedded within the normal densely packed lamellar microstructure, which lacks the detectable gap spacing present in the multilayer region. The characteristic angle θ’ between the local multilayer surface normal and the shell surface normal is marked in two positions (b). For complete description of the shell’s microstructural regions, please refer to Supplementary Fig. 4. (c) TEM image showing the regularity in width and spacing of the mineralized lamellae in the multilayer region. Scale bar, 200 nm. (d) Plan-view z-stack overlay showing the distribution of colloidal particles underneath the multilayer, based on X-ray nanotomography reconstructions. Scale bar, 2 μm. (e) Size distribution of the colloidal particles. (f) Atomic force microscopy height image of the intact colloidal particles, demonstrating their non-faceted fused-granular surface morphology. Scale bar, 100 nm.