Physophoridae

Physophoridae, a sub-order of Hydrozoa belonging to the order Siphonophora (q.v.), including those with a flask-shaped float or pneumatophore, and with two or more rows of the modified individual polypes forming the structures known as nectocalyces, hydrophyllia, and hydrocysts. In the most typical genus Physophora these are borne on a long stem, but there are no hydrophyllia. The members of the group are all marine, and live swimming on the surface of the sea, far from land, in tropical and sub-tropical regions. No fossil representatives are known.