The Hydrostatic Appartus within the Nautiloid Shell

One of the purposes of the siphuncle in Nautilus was to regulate
buoyancy, possibly by adding and removing liquid to and from the camerae.

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.

Figure 12: By propulsion and removing liquid
from the camerae, a Nautilus swims to the surface.

© Sarah Vandervlugt.1998