Differentiation of protoplasm in nummulitidae (Foraminifera) from Elat, Red Sea

Abstract

Chambers and canal system in the shells of Operculina ammonoides (Gronovius) and Heterostegina depressa d'Orbigny contain different protoplasm. The connections between the two main parts of the protoplasmic body are much smaller than the connections from chamber to chamber by the stolo system. The connections between chamber and canal system are located in the marginal sulcus and at the base of the chamber. The chamber protoplast (including the stolo system) is protected by a relatively thick, lamellar, mucopolysaccharide membrane — called organic lining — which represents also the template for the mineralization of the shell. Together, organic lining and shell form the cell wall. Over the pore holes in the lateral chamber walls, the organic lining thins out, but is not perforated. The plasma membrane below the organic lining seems to be differentiated by a bossy surface with comparatively coarse granules. The symbionts are concentrated below the lateral wall of the chambers, nestling against 2 or 3 pore-hole depressions. The differentiation of the organic lining, the plasma membrane below the pore holes, and the position of the symbionts in the chamber plasma point to a physiologic relationship between pores and symbionts. The cell organelles in the chamber protoplasm indicate the mainly metabolic function of the chamber protoplast. The protoplasm in the canal system is covered only by the plasma membrane, and is particularly rich in microtubuli similar to ordinary foraminiferal rhizopods. The canal system is, therefore, interpreted as consisting of a system of invaginations of the cell wall determining the morphology of proximal parts of the pseudopods.