The Collaborative International Dictionary of English v.0.48:

Dracunculus \Dra*cun"cu*lus\, n.; pl. Dracunculi. [L., dim. of
   draco dragon.] (Zool.)
   (a) A fish; the dragonet.
   (b) The Guinea worm (Filaria medinensis).
       [1913 Webster]