hydrobranchiata

from The Century Dictionary.

• In Lamarck's latest classification, a division of gastropods, distinguished from Pneumobranchiata, and containing species which breathe water only. The section imperfectly corresponds to the nudibranchiates, inferobranchiates, and tectibranchiates of Cuvier.

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

• noun plural (Zoöl.) An extensive artificial division of gastropod mollusks, including those that breathe by gills, as contrasted with the Pulmonifera.