Elaboration and ultrastructural changes in the pore canal system of the mineralized cuticle of Carcinus maenas during the moulting cycle.
Two basic structural components are concerned in the elaboration of the pore canal system in the mineralized cuticle of the decapod crab Carcinus maenas: tubular cytoplasmic extensions originating from epidermis and vertical fibres. These components are present from the moment the first procuticular materials of the new cuticle are laid down but their organization varies according to a precise schedule during the further moult cycle stages. Cytoplasmic extensions form a complicated branching system connecting the epidermal layer with all regions of the cullcular compartment, at least transitorily. During the moult cycle the prolongation of this cellular system appears to result from two concomitant but opposite phenomena. Before ecdysis the growth of cell extensions in the proximal cuticular layers prevails over their regression at the distal level. During the post-moult period these phenomena are reversed in importance so that the pore canal system is without cytoplasmic material as soon as intermoult starts. The depositing of vertical fibres takes place in close contact with the proximal cell extension plasma membrane, which never bears dense plaques. As moult stages progress, they are gradually organized into twisted sheaths that persist throughout the intermoult. Incidentally, some fibres invade the pore canal lumen freed from cell extensions. Some aspects regarding the fine organization, the chemical composition and the functional significance of both epidermal tubular extensions or vertical fibres are also discussed in the light of previous investigations carried out on crustaceans and in other arthropods.
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Fellow ('Aspirant') of the Belgian Fonds National de la Recherche Scientifique Belgium.
Goffinet
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