HISTOCHEMISTRY AND ULTRASTRUCTURE OF THE CRYPT CELLS IN THE DIGESTIVE GLAND OF APLYSIA PUNCTATA (CUVIER, 1803)

Abstract

The crypt cells lining the Aplysia punctata digestive tubules comprise of three types of cell; calcium, excretory, and thin cells. The calcium cells play a role in osmoregulation, mineral storage, exocrine secretion, iron detoxification, and excretion processes. They possess well- developed microvilli and a basal labyrinth, suggesting a role in absorption. The Golgi apparatus is involved in the production of two main components of calcium spherules; the fibrillar material and mineralized granules. Golgi complex, rough endoplasmic reticulum (RER), ribosomes, and altered mitochondria are involved in the formation of calcium spherules. Secretory activity is indicated by the formation of dense granules containing iron and calcium salts. Lipofuscin pigment has been found in large concretions which may arise from cytoplasmic areas surrounded by endoplasmic reticulum, RER and Golgi tubules. There are three stages of excretory cells, called early, mature, and post-excretory cells. This study traces the development of granulofibrillar vacuoles up to the formation of the lipofuscin concretions and shows that excretory cells are in fact degenerating calcium cells. The fine structure of thin cells suggests that they are young calcium cells.