The Collaborative International Dictionary of English v.0.48:

abranchious \abranchious\ adj.
   1. having no gills; -- same as abranchiate. branchiate

   Syn: abranchiate, abranchial, gill-less
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

abranchious
    adj 1: having no gills [syn: abranchiate, abranchial,
           abranchious, gill-less] [ant: branchiate, gilled]