Paedonothridae Norton, Ermilov & Bayartogtokh fam. nov. is proposed as a new family of the oribatid mite hyporder Nothrina. It is monotypic, based on Paedonothrus reductus Norton, Ermilov & Bayartogtokh gen. et sp. nov., which was sampled from floating vegetation in a shallow lagoon in Kavaratti Atoll of the tropical Lakshadweep Islands, Arabian Sea, India. As such, it is the first known aquatic oribatid mite that is truly marine. It is easily distinguished by knife-like claws, wide separation of genital and anal valves, and reduction of genital papillae to a single small pair. The latter two are juvenile traits in other nothrines and, considering the many losses of body and leg setae, P. reductus appears to be the most paedomorphic known member of Nothrina. We argue for the inclusion of Paedonothridae in the superfamily Malaconothroidea and present a table of traits differentiating it from Malaconothridae and Trhypochthoniidae. While specimens are few, all are adult females, so P. reductus probably is thelytokous, like all other known members of the superfamily.