pulmograde

from The Century Dictionary.

• Having the characters of the Pulmograda; swimming by means of alternate contraction and expansion of the body, as if by a kind of respiration, as a jellyfish.
• noun An acaleph of the group Pulmograda; a discophorous hydrozoan.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Zoöl.) Swimming by the expansion and contraction, or lunglike movement, of the body, or of the disk, as do the medusæ.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective zoology Swimming by means of expansion and contraction.