The Initiation and Early Stages of Postmolt Mineralization in the Blue Crab, Callinectes sapidus

Abstract

Crabs are encased in a rigid exoskeleton or cuticle that is hardened by both protein crosslinking and calcification. In order to grow, the exoskeleton must be periodically molted. The two outermost layers of the exoskeleton of crabs are deposited prior to the molt, but remain uncalcified until the animal sheds its old exoskeleton. The inhibition of premolt calcification and initiation of postmolt calcification are effected by biochemical changes in the organic matrix. In the 2 h after the molt, sugar moieties are enzymatically altered on cuticular glycoproteins by an N-acetylhexosaminidase secreted by the underlying epithelium. These alterations appear to unmask nucleation sites that allow calcification to commence. The initial deposition of mineral is in the form of amorphous calcium carbonate (ACC). As postmolt calcification continues and the principal layer (endocuticle) is deposited and mineralized, the ACC is largely converted to or overgrown by calcite. Prior to the onset of ACC deposition, silicon has been detected in those areas of the exoskeleton that are about to undergo mineralization. As calcification proceeds, silicon is no longer detected. It is hypothesized that silicon is involved in the stabilization of ACC by destabilizing the crystal lattice of calcite before it undergoes the transition to or is overgrown by crystalline calcite.

Structure of Hard And Soft Carapace Exoskeleton Biomaterial Through SEM-EDXRS at Various Stages of Development Scylla paramamosain Mud Crab

“…SEM-EDXS can analyze powerful materials by classifying objects specifically by considering chemical and physical properties and simultaneously providing information on topography, morphology, and elemental composition of objects. Besides, the advantages of being able to detect and analyze surface fractures, provide information in microstructure, examine contamination of a surface, reveal spatial variations in chemical composition, provide qualitative chemical analysis, and identify crystal structure [24] in the calcification process of cuticles in the postmolt and premolt (D3) [36] blue crab, Callinectes sapidus and cuticle mineralization processes in terrestrial isopods Armadillidium vulgare and Porcellio scaber [37], as well as characterization of minerals accumulated in tissues [38].…”

Moult induction methods in soft‐shell crab production

“…In portunid crabs, the moulting process can be divided into four main stages, that is intermoult, premoult, ecdysis and postmoult (Quinitio & Estepa, 2011; Roer & Dillaman, 2018). The cuticle layers involved during moulting are the epicuticle (outermost), exocuticle, endocuticle and non‐calcified membranous layer (innermost) (Figure 1).…”

“…The cuticle layers involved during moulting are the epicuticle (outermost), exocuticle, endocuticle and non‐calcified membranous layer (innermost) (Figure 1). The outermost epicuticle consists of an organic matrix rich in protein, lipid and calcium salts but without chitin whereas the organic matrix of the inner three cuticle layers is of protein and chitin microfibrils (Roer & Dillaman, 2018). The intermoult stage of portunid crabs is often the longest stage where cuticular formation is completed and the outer exoskeleton is hard – cuticle completely deposited and fully mineralized (Priester et al, 2005) – with minimal sign of epidermis separation from the exoskeleton (Freeman et al, 1987; Mangum, 1985).…”

“…The calcification of the epi‐ and exocuticle (the two outermost cuticle layers) begins in several hours after moulting—postmoult stage (Shafer et al, 1995). Amorphous calcium carbonate, together with α‐chitin and β‐keratin, are deposited along the epicuticle and the inner and outer edges of the exocuticle, giving early strength and stability to the newly moulted crab (Roer & Dillaman, 2018). The construction and mineralization of endocuticle come after the formation of the first two cuticle layers, that is epi‐ and exocuticle (Pratoomchat et al, 2002).…”

“…Mineralization of the exocuticle and the concurrent calcification of the endocuticle continues until a non‐calcified membranous layer is secreted. This marks the end of exoskeleton mineralization and indicates the transition to intermoult stage (Dillaman et al, 2005; Roer & Dillaman, 2018).…”