| abstract | The oribatid family Zetomimidae is represented in North America by the genera Heterozetes and Zetomimus, both widely distributed throughout the Holarctic and Neotropical regions, and the genus Naiazetes, known from eastern North America. Species in these genera are found in semiaquatic to aquatic habitats. Some species show distinct sexual dimorphism. Revised diagnoses are presented for the Zetomimidae and included genera, and a new species, Zetomimus cooki sp. nov., is proposed. Heterozetes aquaticus (Banks), H. minnesotensis (Ewing), Zetomimus francisi (Habeeb), and Z. setosus (Banks) are redescribed and the immatures of H. aquaticus are described. Zetomimus naias Behan-Pelletier is newly recorded from southeastern USA. Heterozetes patchlorum Habeeb is considered a junior subjective synonym of H. aquaticus (Banks), and H. cayugensis Habeeb is considered a junior subjective synonym of H. minnesotensis (Ewing). Identification keys and distribution records are provided for the 3 genera and 7 species of Zetomimidae now known for North America. |