The Collaborative International Dictionary of English v.0.48:

Ceratobranchia \Cer`a*to*bran"chi*a\, n. pl. [NL., fr. Gr.
   ke`ras, ke`ratos, horn + ?, n. pl., gills.] (Zool.)
   A group of nudibranchiate Mollusca having on the back
   papilliform or branched organs serving as gills.
   [1913 Webster]