Distribution of digestive tubules and fine structure of digestive cells of Aplysia punctata (Cuvier, 1803)

Abstract

The distribution of digestive tubules of Aplysia punctata has been studied in animals under experimental feeding conditions. Histological analysis of the digestive gland has revealed two types of tubules, called tubules A and B. Tubules of type A were composed of basiphilic cells (calcium, excretory and thin cells) and tubules of type B were lined by large digestive cells and basiphilic cells. The latter occur in small groups, usually in the corners of the tubules. Type A tubules are involved in ion metabolism and show a diphasic cycle (absorptive and reconstitutive) according to the height and the stage of calcium cells. Type B tubules are involved in digestive processes and display a tetraphasic cycle (holding, absorption, fragrnentative and reconstitutive) depending upon the height and the stage of the digestive cells. The tetraphasic cycle was compared with the four categories of tubules in bivalves, It is proposed that digestive processes may be continuous in digestive cells of A. punctata.