Cytomorphology and function of the pericardial appendages of Nautilus (Cephalopoda, Tetrabranchiata)

Abstract

The pericardial appendages (glands) are the principal excretory organs of the tetrabranchiate cephalopods. They were studied in Nautilus macromphalus and N. pompilius using light and electron microscopical methods. The four organs, which are homologous with the branchial heart complex in Coleoida, appear to represent a phylogenetically archaic state. Actually, they have had to take over the primary functions of secretion, and it will be seen that they are highly evolved. They are built up of numerous contractile villi which can be subdivided into three functionally important areas: the folded peripheral epithelium functioning particularly in reabsorption, the primarily secretory epithelium of the apical infoldings of the villi, and the ovoid cells with foot processes building up an ultra-filtration barrier. The filtrate seems to be expelled into the terminal secretory epithelium of the apical infoldings and not directly into the coelom.