FINE-STRUCTURAL SURVEY OF OLD CUTICLE DEGRADATION DURING PRE-ECDYSIS IN 2 EUROPEAN ATLANTIC CRABS

Light and transmission electron microscopy were used:o monitor changes due to the degradation of the old exoskeleton and related events in t he sclerites, articular membranes, and gills of two decapod crustacean s (Carcinus maenas and Macropipus puber) during pre-ecdysis. In both s clerites and articular membranes, degradation follows a similar genera l pattern in both crab species, while the gill cuticle appears unalter ed, In early pre-ecdysis (D-0), the degradation of the old cuticle sta rts with the secretion of ecdysial droplets by the epidermis. Apolysis , occurring at stage D-1', is re-defined as an event, not necessarily morphologically observable, consisting in the loss of adherence betwee n the epidermis and the old cuticle during early pre-ecdysis of arthro pods, At the stage D(1)triple prime, the moulding of the epidermal cel l surface occurs in preparation to the deposition of the new cuticle a nd causes the opening of the ecdysial cleft, In the principal layer of sclerites, degradation of the chitin-protein microfibres should prece de mineral dissolution, In contrast to the other degraded cuticle laye rs, the membranous layer of sclerites and the innermost endocuticular lamellae of articular membranes are transformed into a digestion-resis tant fibrous network resembling the ecdysial membrane of insects.