Physonects have a pneumatophore and nectosome, which harbors the nectophores used for jet propulsion. Calycophorans differ from cystonects and physonects in that they have two nectophores and no pneumatophore. At the front is the pneumatophore, an orange-coloured, gas-filled float. The pneumatophore develops from the planula, unlike the other polyps. The pneumatophore forms at the opposite end to the mouth. The gas-filled bladder, or pneumatophore, remains at the surface, while the remainder is submerged.