Abstract
The crustacean cuticle consists of a complex organic matrix and a mineral phase. The physical and chemical properties of the cuticle are corellated to the specific functions of cuticular elements, leading to a large variety in its structure and composition. Investigation of the structure-function relationship in crustacean cuticle requires sophisticated methodological tools for the analysis of different aspects of the cuticular architecture. In the present paper we report improved preparation methods that, in combination with various electron microscopic techniques, have led to new insights of cuticle structure and composition in the tergite cuticle of Porcellio scaber. We used thin sections of non-decalcified tergites and decalcified resin embedded material for transmission electron microscopy and scanning transmission electron microscopy. Etched sagittal planes of bulk tergite samples were analysed with field emission scanning electron microscopy. We have found a distinct distal region within the exocuticle that differs from the subjacent proximal exocuticle in the arrangement of fibres. Within this distal exocuticle chitin-protein fibrils assemble to fibres with diameters between 15 and 50 nm that are embedded in a mineral matrix. In the proximal exocuticle and the endocuticle fibrils do not assemble to fibres and are surrounded by mineral individually. Furthermore, we show that the pore canals are filled with mineral, and demonstrate that mild etching of polished sagittal cuticle surfaces reveals regions containing mineral of diverse solubility.
Highlights
The structural organisation of the crustacean cuticle has recently led to increasing interest because of its high structural and chemical variability
The organic matrix of the exocuticle is more intensely stained than the endocuticle one, resulting in a sharp border between them (Figure 1A)
In the proximal exocuticle pore canals are more branched than in the endocuticle and a high variation in the width of pore canals can be observed, probably due to twisting of spindle-shaped pore canals. This leads to an islelike appearance of the part of the organic matrix that is organised in a twisted plywood structure (Figures 1A, B)
Summary
The structural organisation of the crustacean cuticle has recently led to increasing interest because of its high structural and chemical variability. That in some species these planes are formed by fibrils that are not assembled to fibres (Nicolov et al 2011, Seidl et al 2011). Many of these planes are stacked upon another in a way that the direction of the fibrils/fibres is twisted by a small angle against that of the preceding plane, thereby forming a twisted plywood structure (Bouligand 1972). The distance between two planes with parallel fibrils/fibres is called stacking height These stacks form three of the four principal layers of the cuticle: the exocuticle, the endocuticle and the innermost membranous layer. In crustaceans the exocuticle and endocuticle are mineralised by calcite, amorphous calcium carbonate (ACC), and to some degree by amorphous calcium phosphate (Dillaman et al 2005, Boßelmann et al 2007, Neues et al 2007, Hild et al 2008, Neues et al 2011)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
