Chamber Nautilus

Does the Chambered Nautilus originally lives on a big shell or does the shell expand with his membranes ? ?

I know the Chambered Nautilus creates new chambers as it grows but does it originally have such a big shell or is the shell made from the membranes too ? this may not make sense but pls give the info you know

The hatchling has quite a small shell compared to the adult. The outer walls of new chambers and the partitions between old and new chambers are formed by calcareous secretion additions to the shell as the organism grows.

Auto Draw 2: Chambered Nautilus Shell