Sea urchin calcite has a nanoparticulate constitution where the calcite lattice is highly cooriented over large scales (mm to cm) despite several structural/architectural  levels between the unit-cell and the macroscopic scale. Using single-crystal XRD and Electron Backscatter microDiffraction (EBSD) we determined the crystallographic architecture of spines and body plates of the species Paracentrotus lividus and Cidaris cidaris. Within the stereome of the plates, a porous meshwork of calcite and hollow space, the calcite lattice is highly co-oriented in 3D (single-crystal-like) over distances reaching 1mm. Single-crystalline blocks are separated by small-angle boundaries such that the lattice orientation follows the curvature of the tests. For P. lividus the calcite c-axes are radially oriented; for C. cidaris the c-axes are tangential to the surface of the tests. The tubercles (knobs on which the single-crystal-like spines are anchored) form partial spherulites.  The spine of P. lividus shows the same single-crystal-like co-orientational pattern of the biocalcite throughout the 18 segments. Small calcite bridges cross the gaps between the segments. There is a coherence of {10.0} plane normals and the radial axis of every third segment. The bulk of the spine of C. cidaris is stereome-like with single-crystal-like lattice co-orientation. The outside of the single-crystalline C. cidaris spine is lined with 18 protruding buttresses of polycrystalline material.