Fig. 4
Formation of the secretion crust in Charinus acosta. a. Histological section of the integument of a freshly moulted animal (dorsal carapace). Different epidermis cells are present between the cuticle (cut) and the musculature (mus), containing either spherical strongly stained vesicles (ves) or large vacuoles (vac). The 2-lipped major gland openings (maj) are connected to a secretory cell (sce), in which the content of different vesicles is apparently mixed (see Fig. 5). b. An SEM micrograph of the cuticle of a freshly moulted animal shows the absence of the granular secretion coat. c. Histological section of the integument of an inter-moult animal (same scale as in A.). The epidermal cells are reduced in size, the vacuoles shrink, and the stained vesicles are mostly absent. The solidified secretion layer is assembled on the cuticle and consists of a thin continuous layer and globular granules (gra), both of which are highly stained like the vesicles in A. The different in the thickness of the cuticle (cut) if compared to A. is due to the difference in the animal instar. d. Same as in B., showing the assembled secretion crust. e. Appearance of the carapace cuticle at an early stage of secretion emergence (2 h after moulting). Arrowheads indicate the advancing secretion film. The scale-like structures are cuticular formations. f. Appearance of the secretion coat 30 h after moulting (leg cuticle). Globular structures are beginning to emerge. Frequent holes in the secretion film may result from vesicles of a volatile phase, presumably water. g. Appearance of the fully shaped secretion crust, as observed in an exuvia (carapace). h. Detail of the advancing secretion film 2 h after moulting. i–j. Details of the secretion film 30 h after moulting with forming granules. Note that the surface of granules is still smooth and sizes differ. k. TEM micrograph showing a detail of the assembled secretion film after solidification. l–m. Fine structure of a granule. Three layers are distinguishable, an isotropic inner layer, a nano-porous outer layer and 3rd layer of an irregular material