The Collaborative International Dictionary of English v.0.48:

Diphycercal \Diph`y*cer"cal\, a. [Gr. difyh`s double (di- =
   di`s- twice + fy`ein to produce) + ke`rkos tail.] (Anat.)
   Having the tail fin divided into two equal parts by the
   notochord, or end of the vertebral column; protocercal. See
   Protocercal.
   [1913 Webster]