physograda

from The Century Dictionary.

• noun In De Blainville's classification of acalephs, a group of oceanic hydrozoans, provided with hollow vesicular organs which buoy them up and enable them to float.
• noun In a restricted sense, an order or suborder of siphonophorous hydrozoans, represented by such forms as the Physaliidæ: distinguished from the Chondrograda, as Velellidæ. See cut under Physalia.