Diagnoses are presented for the oribatid mite family Tenuialidae, the subfamily Tenuialinae, and the genera Tenuiala, Tenuialoides, Hafenrefferia, and Hefenferrefia. A new subfamily, Peltenuialinae, is proposed, based on Peltenuiala pacijica, n. gen~, n. sp. Hafenrefferiella is considered a junior synonym of Hafenferrefia. The following new combinations are proposed: Hafenferrefia nevesi (Sellnick); Hafenferrefia hyrcanica (Krivolutsky); Tenuialoides translamellatus (Aoki and Fujikawa); Peltenuiala orbiculata (Aoki and Ohnishi). A close relationship is suggested between the Liacaroidea and the Cepheidae.