dorsibranchiate

from The Century Dictionary.

• Having gills on the back; notobranchiate, as certain nudibranchiate gastropods and many marine annelids.
• Specifically, having dorsal gills, as the Dorsibranchiata; of or pertaining to the Dorsibranchiata.
• noun A member of the Dorsibranchiata.

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

• adjective (Zoöl.) Having branchiæ along the back; belonging to the Dorsibranchiata.

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

• adjective zoology Having branchiae along the back; belonging to the Dorsibranchiata.
• noun zoology Any of the Dorsibranchiata.