FINE-STRUCTURE AND MORPHOGENESIS OF THE SCLERITE EPICUTICLE IN THE ATLANTIC SHORE CRAB CARCINUS-MAENAS

Three basic sublayers are identified in the epicuticle of the minerali sed sclerites of the Atlantic shore crab Carcinus maenas (Crustacea, D ecapoda): the surface coat, the cuticulin layer, and the inner epicuti cle. Their morphogenesis and subsequent changes are described througho ut the moulting cycle in the normal cuticle and the cuticular structur es, namely the sensory bristles and epicuticular spines. At first, the cuticulin layer begins to form just after apolysis. This layer is bui lt directly over the plasma membrane and immediately appears as a memb rane-like structure 40 nm thick, composed of five symmetrically arrang ed laminae: two inner electron-lucent leaflets sandwiched between two thick electron-dense leaflets and separated by a thin dense median str atum. Elaboration of the inner epicuticle below the cuticulin layer is thought to occur via an intussusceptive process involving the pore ca nal cell extensions as transport routes. The inner epicuticle is made of vertically oriented microfibres embedded. in an electron-dense matr ix material. During the second half of the premoult period, the surfac e coat is deposited on the upper side of the cuticulin layer.