Oribates (Acariens) des lichens crustacés d’Argentine I. Pirnodus cryophilus n. sp. - Description is made of a new species: Pirnodus cryophilus (Acari, Oripodidae), an inhabitant of crustaceous lichens on the eastern slope of ’Cordon del Plata’, frontal cordillera, Mendoza, Argentina, 3,200 meters high. The complete ontogenetic cycle is studied and comparison is made with other species of the same genus (P. detectidens and P. soyeri); besides, data on behaviour and feeding preferences are provided.