Source : Webster's Revised Unabridged Dictionary (1913)

Epizoon \Ep`i*zo"["o]n\, n.; pl. {Epizoa}. [NL., fr. Gr. 'epi`
   upon + ? animal.] (Zo["o]l.)
   One of the artificial group of invertebrates of various
   kinds, which live parasitically upon the exterior of other
   animals; an ectozo["o]n. Among them are the lice, ticks, many
   acari, the lerneans, or fish lice, and other crustaceans.

Source : WordNet®

epizoon
     n : any external parasitic organism (as fleas) [syn: {ectoparasite},
          {ectozoan}, {ectozoon}, {epizoan}]