Life-cycle and functional cytology of the hepatopancreatic cells of Astacus astacus (Crustacea, Decapoda)

Abstract

The hepatopancreas of the freshwater crayfish Astacus astacus was reinvestigated by means of light and electron microscopy using refined techniques of tissue preservation. The results contribute significantly to the solution of controversial problems of the decapod hepatopancreas such as cell genealogy, cellular interdependences, elimination of senescent cells and functional interpretation of the cell types. The three mature cell types of the organ, R-, F- and B-cells, are shown to originate independently from embryonic E-cells which are located at the blind-ending tips of the hepatopancreatic tubules. The less abundant M-cells are supposedly of non-hepatopancreatic origin since they are also found in other epithelia of the digestive tract. Differentiating cells can be assigned at an early stage to one of the three hepatopancreatic cell lines if the ultrastructural appearance and distribution pattern of their organelles are used as distinguishing features. The most sensitive markers are the Golgi bodies which have a cell-specific architecture and secretion product not only in mature cells but also in early differentiating stages. Later conversion of one cell type into another, as has often been proposed in literature, does not occur. Senescent cells are preferably expelled from the epithelium at the junction of neighbouring hepatopancreatic tubules and at the antechamber which links the hepatopancreas to the main digestive tract. Cellular discharge in the antechamber occurs by sliding of the oldest parts of the hepatopancreatic epithelium across a particular antechamber epithelium that was thus far unknown. New ultrastructural findings are described with respect to the absorptive apparatus of nutrient absorbing R-cells, the formation of Golgi vesicles and retrieval of membranes in digestive enzyme synthesizing F-cells, and the involvement of Golgi body and endoplasmic reticulum in the formation of heterophagic vacuoles in B-cells. The discovery of these ultrastructural features enables a more sophisticated functional interpretation of the hepatopancreatic cells of Decapoda.