A correlated light and electron microscopic study of the structure and secretory activity of the accessory salivary glands of the marine gastropods, Conus flavidus and C. vexillum (neogastropoda, conacea)

Abstract

The structure and secretory activity of the accessory salivary gland in two species of Conus were examined using routine and histochemical techniques of light, scanning and transmission electron microscopy. The composite layers of the accessory salivary gland of Conus are a luminal epithelium, fibromuscular layer, submuscular layer, and a capsule. In C. flavidus and C. vexillum, the luminal epithelium is formed by epitheliocytes and cytoplasmic processes extending from the secretory cells, whose perikarya form the submuscular layer. The processes carry secretory cell products (chiefly Golgi-derived glycoprotein) across the fibromuscular layer and terminate between epitheliocytes (at the bases of the secretory canaliculi) or beyond the surface of the epithelial cells. Conus vexillum is distinguished from C. flavidus by its high content of lipofuscin. Epitheliocytes are the only microvillated cells in the accessory salivary gland of Conus. In C. flavidus, epitheliocytes extrude secretory granules, various types of cytoplasmic blebs and clear vesicles by apocrine "pinching off." Clear vesicles are shed from the tips of microvilli. The luminal epithelial cells of C. vexillum similarly egest clear vesicles, but normally undergo additional holocrine secretion to release lipofuscin. The secretions of epitheliocytes appear to be major products of the accessory salivary gland: consideration of secretory activities by both epitheliocytes and secretory cells will therefore be necessary when directly investigating accessory salivary gland function in Conus.

Ultrastructural and histochemical study of the salivary glands of Aplysia depilans (Mollusca, Opisthobranchia)

“…1996). In prosobranchs, salivary glands can contain just two types of secretory cells (Andrews 1991; Benmeradi and Benmeradi 1992), but neogastropods possess accessory salivary glands containing additional cell types (Schultz 1983; Andrews 1991).…”

Light and electron microscopic study of the anterior oesophagus of Bulla striata (Mollusca, Opisthobranchia)

“…This association between cilia and apocrine secretion suggests that those cilia serve to propel the aposomes towards the posterior part of the oesophagus, avoiding their accumulation on top of the cells that produce them. In gastropods, apocrine secretion was previously reported in the digestive tract (Bush 1989; Leal‐Zanchet 1998) and associated glands (Schultz 1983; Andrews 1991; Andrews and Thorogood 2005). In Deroceras reticulatum Müller, 1774, a terrestrial slug, the formation of apical blebs in crop epithelial cells was observed only after ingestion of molluscicides, and not in control animals (Bourne et al .…”

Ultrastructural and histochemical study of the salivary glands of Aplysia depilans (Mollusca, Opisthobranchia)

“…Three types of secretory cells were observed in the salivary glands of A. depilans, while in several pulmonates four or more types of secretory cells have been reported (Boer et al 1967;Walker 1970;Beltz and Gelperin 1979;Moya et al 1992;Serrano et al 1996). In prosobranchs, salivary glands can contain just two types of secretory cells (Andrews 1991;Benmeradi and Benmeradi 1992), but neogastropods possess accessory salivary glands containing additional cell types (Schultz 1983;Andrews 1991).…”