The eggcase contains a bubble of air that the animal captures at the surface of the water and uses for buoyancy , similarly to other shelled cephalopods , although it does not have a chambered phragmocone as do other shelled cephalopods .
The egg case also contains a bubble of gas used for buoyancy similar to shelled cephalopods , although it does not have chambers as seen in other shelled cephalopods .