In contrast to synthetic materials, materials produced by organisms are formed in ambient conditions and with a limited selection of elements. Nevertheless, living organisms reveal elegant strategies for achieving specific functions, ranging from skeletal support to mastication, from sensors and defensive tools to optical function. Using state-of-the-art characterization techniques, we present a newly found biostrategy for strengthening and toughening the otherwise brittle calcite optical lenses found in the brittlestar Ophiocoma wendtii . This intriguing process uses coherent nanoprecipitates to induce compressive stresses on the host single crystalline matrix, functionally resembling the Guinier–Preston zones known in classical metallurgy. The characterization techniques used include high-resolution powder x-ray diffraction , submicrometer scanning x-ray diffractometry, nanotomography, XANES and PEEM and aberration corrected HRTEM.  The formation of these GP-zone-like domains do not form via heating followed by supersaturating via quenching as in classical metallurgy but rather the supersaturation is achieved by the crystallization of magnesium calcite via a magnesium rich amorphous precursor phase.   In addition, the magnesium-rich nano precipitates are found to be present in layers with alternating density which can be clearly seen by diffraction as well as by nanoCT imaging . The effect of these layers on the mechanical properties will be discussed. We will also discuss the lessons we can learn from the brittlestar in toughening and strengthening man-made engineering materials in a bioinspired manner.