Next the pit closes up to form a vesicle with a pore, and so gives rise to the pneumatophore.
In cases where the cormus has no pneumatophore the topmost swimming bell may contain an oil-reservoir or oleocyst.
The one end forms the pneumatophore, and the other, the oral part, the polypite.
Divergent views have been held as to the morphological significance of the pneumatophore.
If sterile they remain attached and locomotor in function, forming the nectosome, the pneumatophore and swimming-bells.