La variabilite chaetotaxique et la neotrichie gastronotique des Hydrozetidae (Oribates). - The chaetotaxic variability and gastronotic neotrichy of a new species, Hydrozetes escobari Fernandez and a new subspecies H. dimorphus virginalis Fernandez, from Argentina, are studied. The priority among the setae c of the notogaster is clarified. This pattern is shown to be different from european species of the genus Hydrozetes. The neotrichy of the posterior gastronotic setae is very close to members of the genus in Europa but in south american taxa this phenomenon begins from the Jarval instar. This case is very rare in Oribatid mites.