The present study aimed to develop taxonomic keys to the world species of the genus Bryobia, categorized into three subgenera: Allobia Livschits & Mitrofanov, Bryobia s. str. Koch, and Lyobia Livschits & Mitrofanov. Published descriptions, redescriptions, and illustrations of a total of 149 world species were thoroughly analyzed. The taxonomic notes on the status of the species in the species groups of each subgenus are discussed in detail. The variability of morphological characters found among different populations of a species is discussed. As a result, 116 species of the genus Bryobia were classified in three diagnostic keys, with 22, 43, and 51 species assigned to the three subgenera Allobia, Bryobia, and Lyobia, respectively. The population of B. neoribis Tuttle & Baker from Utah, USA, should be re-identified through type examination due to differences from the original description of the species. Additionally, taxonomic notes are provided on the status of the remaining 33 species, and arguments are provided on suggested synonyms among them.

Four new species groups of the Tenuipalpus sensu lato group are proposed in the present study based on the total number of dorsal opisthosomal setae, namely, carolinensis with ten pairs of setae (214 species), dubinini with nine pairs of setae (33 species), granati with eight pairs of setae (29 species), and barticanus with seven pairs of setae (7 species) Additionally, diagnostic keys to species groups and 273 species of the Tenuipalpus sensu lato are provided. Three species, T. lustrabilis Chaudhri, T. guptai Sadana and Gupta, and T. solanensis Sadana and Gupta, are synonymized with T. punicae Pritchard and Baker. One species, T. rodionovi Chalilova, is suggested as a junior synonym of T. granati Sayed, and eight species, T. chiococcae De Leon, T. costarricensis Salas and Ochoa, T. ephedrae Livschitz and Mitrofanov, T. molinai Evans, T. santae Manson, T. simplychus Cromroy, T. tetrazygiae De Leon, and T. oxalis (Flechtmann), belonging to the carolinensis species group, are not included in the key. Furthermore, a new species of Tenuipalpus sensu lato, T. jazanensis sp. nov., is described and illustrated based on females collected from the Chamaerops spp. (Arecaceae).

Two new predatory mites of the genus Agistemus Summers (Acari: Prostigmata: Stigmaeidae) namely A. neocollyerae n. sp. and A. arabensis n. sp. are described and illustrated based on adult females. Additionally, two species namely A. simplex González-Rodriguez and A. floridanus González-Rodriguez are reported as new records for the stigmaeid mite fauna of Saudi Arabia. A regional key to reported species of the genus Agistemus is also provided.

A new species of Tenuipalpus (Acari: Tenuipalpidae), Tenuipalpus farasanensis sp. nov., is described and illustrated based on female and male specimens collected from Salvadora spp. (Salvadoraceae). The discovery of this species leads to the proposal of a new species group, farasanensis, under Tenuipalpus sensu lato, characterized by six pairs of opisthosomal setae. In addition, four Tenuipalpus species, T. combreti Meyer, T. emeticae Meyer, T. tamarixi Mahdavi and Asadi, and T. viticola Al-Gboory, are reported from Saudi Arabia for the first time. Complementary descriptions of T. combreti and T. emeticae are also provided.

The present research reevaluates the diagnostic characters of Dolichonobia Meyer and demotes it to a subgenus of Mesobryobia . Consequently, Mesobryobia is divided into two subgenera: Mesobryobia (Mesobryobia) and Mesobryobia (Dolichonobia), differentiated by the shape of the peritremes: anastomosed and simple, or bifurcate, respectively. Furthermore, a new species, Mesobryobia (Mesobryobia) neobrevillosa sp. nov ., is described and illustrated based on females collected from grasses (Poaceae) in Jazan Province, Saudi Arabia. Additionally, a key to all species of the genus Mesobryobia is provided.

A new species of the genus Colopalpus Pritchard and Baker, C. neoemeticae sp. nov., is described and illustrated based on females and a male collected from Crotalaria sp. (Fabaceae) in the southwestern region of Saudi Arabia.