If this is the significance of septa in the nautilus, the same must be said of all nautiloid shells, and the families of Ammonites and Orthoceratites; and as the structure of the phragmacone of Belemnites is essentially similar, it must also be applied to such debranchiate shells as are chambered.
1883, William Miller, The Heavenly Bodies: Their Nature and Habitability, Hodder, page 197:
The Debranchiate Cephalopods appear with equal apparent suddenness on the older Mesozoic deposits, and no known type of the Palæozoic period can be pointed to as a possible ancestor.
Sectioned buccal masses of several debranchiate cephalopods prepared by Mrs. von Boletzky were studied with the help of S. von Boletzky at the Laboratoire Arago in Banyuls-sur-Mer.