Cytology of the renal appendages of Nautilus (Cephalopoda, Tetrabranchiata).

The renal appendages of tetrabranchiate cephalopods, Nautilus pompilius (L.) and Nautilus macromphalus (G.B. Sow.), were studied using light- and electron-microscopical methods. The appendages, homologous to the renal appendages of dibranchiate cephalopods, possess in both species a folded transporting epithelium characterized by a secreting brush border and a high content of mitochondria and lysosome-like dense bodies as well as a basal labyrinth, and are separated from the blood lacunae by a multilayered lamina basalis. In the extracellular crypt-like infoldings of the epithelium, numerous concentric stratified concrements are found. The results strengthen the hypothesis that these concrements represent mineral-storage structures only found in calcium shell-supporting species within the class Cephalopoda.