The Structure and Mineralization of the Carapace of the Crab (Cancer pagurus L.) 2. The exocuticle

Abstract

The exocuticle of the dorsal carapace of the intermoult Cancer pagurus was studied by means of light microscopy, electron microscopy, and contact microradiography. In the exocuticle a 5‐15 μm wide highly mineralized external zone was seen where prisms were not present. The cross‐sectional shape and diameter of the prisms varied. The prisms were separated by interprismatic areas varying in width and in degree of mineralization. With increasing width of the interprismatic areas the diameter of the prisms decreased. The prism‐less external zone may be the result of complete mineralization of the prisms. The pore canals of the exocuticle were circular in cross section and present both within the prisms and within the interprismatic areas. The lamellar system of the exocuticle was built up by layers of horizontal fibrils which were interconnected by vertical or oblique fibrils. The minerals of the external prism‐less zone occurred as aggregates of crystalline matter or as large brick‐like structures. Crystal edge lengths up to 300 nm were measured. In well mineralized interprismatic areas aggregates of crystals and relatively large crystals were observed. In poorly mineralized interprismatic areas small plate‐like crystals occurred. Occasionally a prism‐less zone was seen near the exocuticle/endocuticle junction.