The Collaborative International Dictionary of English v.0.48:

Pseudobranchia \Pseu`do*bran"chi*a\, n.; pl.
   Pseudobranchi[ae]. [NL. See Pseudo-, and Branchia.]
   (Anat.)
   A rudimentary branchia, or gill. -- Pseu`do*bran"chi*al, a.
   [1913 Webster]