The external morphology of 2 closely related mite families, Cloacaridae and Epimyodicidae (Acari: Prostigmata), comprising highly specialized endoparasites of vertebrates, is analyzed. These mites exhibit strong regression of many structures ancestrally present in other Prostigmata as a consequence of their endoparasitic mode of life. The relationships of these 2 families with other taxa in the infraorder Eleutherengona are still not clear. Our reinterpretation of the chelicerae as unfused precludes inclusion of this lineage in the Cheyletoidea as proposed previously. A new superfamily, Cloacaroidea superfam. nov., incertae sedis, within the infraorder Eleutherengona is established for these 2 families, and their host–parasite relationships are briefly discussed. A new cloacarid species, Caminacarus dawsoni n. sp., from Graptemys pseudogeographica (Testudines: Emydidae) from the United States is also described.