Der kammerbauvorgang der großforaminifere Heterostegina depressa (Nummulitidae)

Chamber formation of Heterostegina depressa d'Orbigny 1826 mostly starts with the beginning of the daily light period. First, the necessary space for the construction of the new chamber (“Kammerhof”) is provided by rotation of the test inside the ectoplasm sheath, which is well fixed to the substrate. At the same time, protoplasm flows out of the aperture and out of the pores of the last chamber transporting organic particles. Three to 4 h after beginning of chamber formation, these particles coalesce to an organic layer between the ectoplasm sheath and the edge of the test. A short time later, this layer is bound on the outside by an organic membrane. Organic layer and organic membrane indicate the contour of the new chamber together with its chamberlets; they represent the “anlage” of the new chamber. Calcification takes place at this membrane. After the beginning of calcification, which lasts 15 to 20 h, the organic layer is removed and the ectoplasm sheath is retracted to the test.