Ultrastructure of the Midgut Cells of Some Parasitic Copepods with Special Reference to the Secretion of Digestive Enzymes

Abstract

The ultrastructure of midgut cells of six species of parasitic copepods was observed. The anterior zone of the midgut of Conchyliurus quintus, Ostrincola koe, Panaietis yamagutii, Neoergasilus japonicus and Lernaea cyprinacea consisted of vacuolar cells and non-vacuolar cells. The vacuolar cells were characterized by sizable endocytotic and secretory vacuoles suggesting active absorptive and secretory functions, respectively. The secretory product containing digestive enzymes was discharged by holocrine secretion. The non-vacuolar cells were characterized by the well-developed microvilli suggesting an absorptive function of the cells. In Pseudomyicola spinosus, however, the anterior zone of the midgut consisted of non-vacuolar cells only containing numerous primary lysosome-like vacuoles. Such lysosome-like vacuoles situated just underneath the free surface and the well-developed microvilli of the non-vacuolar cells suggested their secretory and absorptive functions. Numerous bacteria occurred consistently in the anterior zone of the midgut of Ps. spinosus. © 1991, The Japanese Society of Fisheries Science. All rights reserved.