dipleurobranchia

from The Century Dictionary.

• A superfamily of nudibranchiate gastropods, having foliaceous branchiæ situated in a fold on each side, and no shell, and containing the families Phyllidiidæ and Pleurophyllidiidæ, which are thus contrasted with Monopleurobranchia. The group is also called Inferobranchiata or Hypobranchiata.