Electron microscopy and synchrotron Bragg diffraction were used for the investigation of the structure of the exoskeleton of the lobster Homarus americanus. The study reveals a pronounced microstructure hierarchy and a strong crystallographic and topological texture of the a-chitin protein network underlying the twisted plywood (Bouligand) structure. The results suggest that the classical picture of such structures must be refined. Instead of a smoothly misoriented stacking sequence of its constitutive nanofibrous chitin-protein planes, two major and two minor orientation branches of the fibers perpendicular to a common < 0 2 0 > crystallographic axis pointing towards the surface of the cuticle were found. This crystallographic texture confirms the microscopical observation that the chitin-protein arrays which form the structural subunits of plywood patterns assume the form of planar honeycombs. (c) 2005 Elsevier B.V. All rights reserved.