Epizoon
Epizoon , noun
[New Latin, from Greek 'epi` upon + zw^,on animal.]
(Zoology) One of the artificial group of invertebrates of various kinds, which live parasitically upon the exterior of other animals; an ectozoon. Among them are the lice, ticks, many acari, the lerneans, or fish lice, and other crustaceans.