In this study we present experimental investigations on the microscopic structure, constituent phases, and crystallographic textures of the exoskeleton of three types of decapod crustaceans, namely, lobster, crab, and horseshoe crab. The carapace of such animals is a biological multiphase nano-composite consisting of an organic matrix (crystalline chitin and non-crystalline proteins) and biominerals (calcite, phosphate). The synchrotron measurements of the crystalline chitin and of the biominerals which are embedded in the chitin-protein matrix (in case of lobster and crab) reveal strong textures. The horseshoe crab does not seem to contain notable amounts of crystalline minerals. The Debye-Schemer images of the lobster specimen suggest that the biominerals form clusters of crystals with similar crystallographic orientation. TEM images support this suggestion. The crystallographic texture of the chitin is arranged with its longest cell axis parallel to the normal of the surface of the exoskeleton.