One of the purposes of the siphuncle in Nautilus was to regulate
The weight of the Nautilus shell at maturity was almost equal to,
but slightly heavier than sea water; so its vertical movement was
controlled by active swimming.
Young shells apparently had positive buoyancy and water was retained in
the camerae until the shell was heavy enough to keep the animal down.
buoyancy, possibly by adding and removing liquid to and from the
camerae.
Figure 12: By propulsion and removing liquid
from the camerae, a
Nautilus swims to the surface.