The direction of beta-chitin deposition in the tube of tubeworm Lamellibrachia satsuma was investigated by texture analysis using X-ray diffraction. The beta-chitin crystallite in the tube has planar orientation with the (1 I 0) plane perpendicular to the surface, and the c-axis is aligned parallel to the tube. The monoclinic unit cell of beta-chitin allowed determination of the sense of c-axis from the orientation of (0 1 0) and (1 0 0) planes. This means that the reducing end of beta-chitin is pointing up in the tube. This orientation can be ascribed to possible secretion mechanisms of the beta-chitin microfibrils, i.e. the chitin-synthesizing enzyme complex travels unidirectionally from top to bottom when the worm body contracts in the tube. (C) 2013 Elsevier Inc. All rights reserved.