Source : Webster's Revised Unabridged Dictionary (1913)

Hydrobranchiata \Hy`dro*bran`chi*a"ta\, n. pl. [NL., fr. Gr.
   "y`dwr water + ? gills.] (Zo["o]l.)
   An extensive artificial division of gastropod mollusks,
   including those that breathe by gills, as contrasted with the
   Pulmonifera. -- {Hy`dro*bran"chi*ate}, a.