The microstructures of the carapaces of the spider crabs Schizophrys dahlak and Hyastenus hilgendorfi were examined under both scanning and transmission electron microscopes. Image analyses of the cross-sectioned carapaces showed that both species have a hierarchical microstructure with three well-defined layers. The two innermost layers (exocuticle and endocuticle) consist of stacked fibers arranged in a twisted plywood fashion producing a "Bouligand structure". They have a similar structure but different thicknesses and height of the stacks. The cuticles are inter-stitched with pore canals of varying width between the studied species, running transversely to the layered structure. This variation in the width of the pore canals in the two species seems to be proportional to the size of the carapace and its surface area.