The Holothyrida are a small group of parasitiform mites with a strong Gondwanan distribution, particularly the Central and South American family Neothyridae and the Australian and New Zealand family Allothyridae. Herein, we describe a new genus of Neothyridae, Amerothyrus gen. nov. Vázquez & Seeman, based on two new species—Amerothyrus ecuatorianus sp. nov. Vázquez & Seeman and Amerothyrus andesianus Vázquez & Seeman sp. nov., both collected from Ecuador. The new genus draws the families Allothyridae and Neothyridae closer together, as the new genus has a peridium, an unusual structure shared with the Allothyridae. We show that, in all other respects, the new taxon belongs within the Neothyridae, and regard the peridium as a regressed plesiomorphy in the new genus. In particular, the peridium is markedly smaller and, in one of the species, present only in the female. We also describe the deutonymph and tritonymph of A. ecuatorianus. Keys are provided to families and genera of Holothyrida and to species of Neothyridae.