Comparative structure and ultrastructure of the midgut and hepatopancreas of five species of Mysidacea (Crustacea): functional implications

Abstract

Comparative structural, ultrastructural, and cytochemical studies were made of the midgut and hepato pancreas of five species belonging to the two suborders of the order Mysidacea, the Lophogastrida and Mysida, under different feeding conditions to investigate their role in digestive processes. Nutritional experiments were also carried out to complete the study. The midgut shows structural differences between the two suborders. The epithelium is composed of a single cell type that is implicated in absorption and production of peritrophic membranes. The intestinal epithelium lies on a characteristic three-layered basal lamina, the thickness of which would increase the strength of the intestinal wall for peristaltis and for transport of fecal pellets. The hepatopancreas displays marked structural differences between the suborders, and the cell distribution is better ordered in Mysida. Absorptive R-cells play an important role in lipoprotein metabolism. B-cells are implicated in intracellular digestion, as is attested to by the presence of a typical vacuolar apparatus. The total absence of the F-cell, considered to secrete enzymes in the Decapoda, raises the question of the origin of the enzymes necessary for extracellular digestion. A review of the cell affiliations of the hepatopancreas in the Mysidacea is required.