THE DEPOSITION OF SKELETAL STRUCTURES IN THE CRUSTACEA. I. THE HISTOLOGY OF THE GASTROLITH SKELETAL TISSUE COMPLEX AND THE GASTROLITH IN THE CRAYFISH, ORCONECTES (CAMBARUS) VIRILIS HAGEN—DECAPODA

Abstract

Histological changes which are associated with the formation of non-calcified skeletal components of the gastrolith discs and those involved in the synthesis and calcification of the gastrolith itself have revealed that: (1) The cuticular surface of the completed gastrolith disc (Stage C4), which forms part of the lining of the stomach, is composed of a thin epicuticle, formed before molt; a thicker, laminated exocuticle, neither crossed by pore canals nor tegumental ducts, formed following molt and completed during Stage B; and an endocuticle, also lacking pore canals and tegumental ducts and characterized by the presence of round, chemically complex, granules without structure, embedded in a loose fibrous meshwork. (2) As gastrolith deposition begins (Stage Do), the epidermis increases in height, becomes branched and attenuated apically, invaginates, synthesizes, elaborates, and calcifies the gastrolith matrix. The gastroliths increase in thickness from around 300 [mu] (Stage Do) to 3[long dash]4 mm (Stage D4). Concomitant with these changes, is an increase in the number of reserve cells in both the epidermis and connective tissue, and a stretching, and thus compression of the sub-epidermal connective tissues, the latter process being correlated with the increasing size of the forming gastroliths. Near the end of Stage D4, the epidermis completes the synthesis of each gastrolith, retracts from it, undergoes a spurt of growth (accompanied by much folding), and then begins to synthesize the epicuticle, the only pre-exuvial cuticular component deposited in this site. Following this synthesis, correlated with the many tasks the epidermis performs throughout the animal, molting ensues and the old stomach lining and the completed gastroliths are released into the stomach. (3) Postmolt changes in the gastrolith disc (Stage A-C) are associated with continued synthesis and secretion of cuticular components, which are completed in Stage O4, from which the entire histological cycle repeats itself.