Discovery of Extranephridial Podocytes in Isopods

Abstract

AB S T R A C T In the fresh-water isopod crustacean Asellus aquaticus podocytes have been discovered laterally within the pericardium, in the blood sinus leading from the pleopods to the pericardium, and, in anterior thoracic segments, above the insertion of the appendages. Similar cells are also present in the pleon of Porcellio scaber. The ultrastructure of these cells resembles that of endsac cells of the crustacean end sac and of arthropod nephrocytes. No lumen or duct is present. These podocytes also resemble those present in decapod gills and may have the task of breaking down hemolymphatic substances. Podocytes are cells consisting of a perikaryon and radiating processes, which bear on the cell surface small cytoplasmic projections (pedicels) resting on a basement membrane. The pedicels from different processes are intimately interdigitated, though separated by regular intercellular spaces. These clefts between the pedicels are closed by an electron-dense extracellular membrane (diaphragm), which separates the extracellular fluid from the spaces of the podo