inferobranchiata

from The Century Dictionary.

• In the old systems of De Blainville and Cuvier, an order of nudibranchiate gastropods having lamellar gills under an expanded mantle, as the families Phyllidiidæ and Diphyllidiidæ.
• In later systems, a suborder of nudibranchiates extended to include forms without branchiæ, but otherwise resembling the typical forms. Thus extended, the order embraces the families Phyllidiidæ, Hypobranchæidæ, Pleurophylliidæ, and Dermatobranchiidæ.
• Also called Inferobranchia, Hypobranchia, Hypobranchiata, Dipleurobranchia.

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

• noun plural (Zoöl.) A suborder of marine gastropod mollusks, in which the gills are between the foot and the mantle.