Morphology and Cyclic Activity of the Digestive Gland ofZidona dufresnei(Caenogastropoda: Volutidae)

Abstract

Zidona dufresnei is a carnivorous snail that plays an important role in the trophic web as a top predator. It is a threatened species due to high levels of fisheries exploitation. In this study, we describe the morphology of the digestive gland of Z. dufresnei from Mar del Plata, Argentina, and discuss the function and the cycle of activity of the different cell types. Histological analysis reveals two types of tubules: type 1 tubules composed of digestive and basophilic cells and type 2 tubules lined by basophilic cells only. Pyramidal basophilic cells contain lipofuscin and a large amount of rough endoplasmic reticulum, which suggests that these cells are responsible for the secretion of digestive enzymes that initiate the extracellular digestion of the food. Columnar digestive cells exhibit large membrane-bound vesicles that contain proteoglycans, neutral glycosaminoglycans and small amounts of lipid and lipofuscin. The presence in digestive cells of many endocytic vesicles and residual lysosomal bodies, as evidenced by the presence of lipofuscin pigments in the apical region, indicate that digestion is completed intracellularly within these cells. The digestive cells are subject to cyclical changes involving four phases: initial, digestion, fragmentation, and disintegration stages.