The Collaborative International Dictionary of English v.0.48:

Dibranchiata \Di*bran`chi*a"ta\, n. pl. [NL., fr. Gr. di- =
   di`s- twice + ? gills.] (Zool.)
   An order of cephalopods which includes those with two gills,
   an apparatus for emitting an inky fluid, and either eight or
   ten cephalic arms bearing suckers or hooks, as the octopi and
   squids. See Cephalopoda.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Dibranchiata
    n 1: comprising all living cephalopods except the family
         Nautilidae: the orders Octopoda (octopuses) and Decapoda
         (squids and cuttlefish) [syn: Dibranchiata, subclass
         Dibranchiata, Dibranchia, subclass Dibranchia]