The genus Thyreophagus is distributed worldwide, containing species occurring in stored food, house dust, bark, subcortical habitats, scale insect associations, and nests of wasps and bees. As species of this genus prefer concealed habitats, the actual species diversity is currently underappreciated. In addition, some described taxa are poorly known and their species boundaries are not entirely clear. Only a few species are known from both adult and deutonymphal stages. Using high-resolution light microscope and scanning electron microscopy, we describe a new partenogenetic species, Thyreophagus calusorum sp. n. from Florida (USA) based on adult stage (female) and heteromorphic deutonymph. This species was reared in the lab and its morphological variation was also studied. We did not find any substantial variation in the shape of the female spermatheca, but in the heteromorphic deutonymph, we did find extensive variation in the shape of tibial setae hT I (a taxonomically important character). Furthermore, we summarized taxonomic data and compiled an annotated checklist of species of Thyreophagus, with 35 species-level taxa. We clarified the following nomenclatorial questions: type species designation in Monieziella Berlese, 1897 was done by A. Berlese in G. Leonardi 1900 (Tyroglyphus entomophagus Laboulbène) not by A. Jacot (1936) as it was though previously; Monieziella mali Berlese, 1897 is an unjustified emendation and junior objective synonym of the name Acarus malus Shimer, 1868, currently Hemisacoptes malus (Shimer, 1868). Three subspecies of Thyreophagus were elevated to the species status due to their distinct morphology: Thyreophagus italicus Vacante, 1989, stat. nov. (=Thyreophagus entomophagus italicus Vacante, 1989); Thyreophagus mauritianus (Fain, 1982), stat. nov. (=Michaelopus gallegoi mauritianus Fain, 1982), and Thyreophagus ponticus Kadzhaya, 1973, stat. nov. (=Thyreophagus entomophagus ponticus Kadzhaya, 1973).