*epizoon*

‖n.; pl. Epizoa [ NL., fr. Gr. 'epi` upon + zw^, on animal. ] (Zoöl.) One of the artificial group of invertebrates of various kinds, which live parasitically upon the exterior of other animals; an ectozoön. Among them are the lice, ticks, many acari, the lerneans, or fish lice, and other crustaceans. [ 1913 Webster ]