The Collaborative International Dictionary of English v.0.48:

bladdernose \blad"der*nose\ n.
   a medium-sized blackish-gray seal (Cystophora cristata)
   with a large inflatable sac on the head; of Arctic-Atlantic
   waters.

   Syn: hooded seal.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

bladdernose
    n 1: medium-sized blackish-grey seal with large inflatable sac
         on the head; of Arctic and northern Atlantic waters [syn:
         hooded seal, bladdernose, Cystophora cristata]