The current knowledge of the Collembolan fauna of Thailand is reported here, based on the checklist of Bedos (1994) completed by data on several taxa described since this date, with an update of the taxonomic status of the species. A total of 194 species from 53 genera and 14 families are listed, that were mostly discovered and described during the last three decades. The updated checklist illustrates a strong unevenness in sampling efforts across space and habitats, and in the degree of taxonomic coverage of the different families of the group. Geographically, only the Doi Inthanon massif can be considered as relatively well known, but even there the species in several major habitats and microhabitats have not been sampled. Data are lacking or much more limited for all other regions of the country. The species richness of Thailand is undoubtedly much more than observed number.

The genus Cyphoderopsis Carpenter is recorded for the first time from continental Southeast Asia, with four new species described from Peninsular Thailand. New characters of taxonomic importance are introduced. The new species herein described are distinguished from other species of the genus by the following combination of characters: dens with two rows of spines, absence of eyes and pigment, and claw with inner teeth. They differ among them in the number of inner teeth on claw, morphology of tenent hairs (pointed versus clavate), number of dental spines and number of central macrochaetae on Th.II (3+3 versus 4+4). The genus Cyphoderopsis in Thailand is shown to be restricted to the South of the Isthmus of Kra, while the closely related genus, Troglopedetes Absolon, replaces it further north, providing new evidence that the Isthmus of Kra is an important biogeographical boundary in Southeast Asia. A checklist and a key to world species of the genus are given.

Three new species of the genus Coecobrya are described from caves in the Thai Peninsula for the first time: C. cavicta sp. nov. and C. polychaeta sp. nov. from Satun Province, and C. chumphonensis sp. nov. from Chumphon Province. These species differ in antennal length, clypeal chaetae, labial palp, sublobal chaetae of maxillary outer lobe, labial and postlabial chaetae, claw, ventral tube, manubrial plaque, and dorsal cephalic and tergal chaetotaxy. They are similar to C. annulata Zhang, Bedos & Deharveng, 2016 but differ from the latter in the combination of antennal length, claw and dorsal chaetotaxy. DNA barcoding COI sequences are provided for two species and three populations and key to the Thai species is also given. One population, which exhibits a great genetic distance (0.219–0.239) and minor but stable morphological differences from C. polychaeta sp. nov., cannot be accepted as a full species as the evidence is insufficient.

This study demonstrates for the first time the presence of marine‐associated mites in the Andaman Sea and Strait of Malacca and reveals a relatively high diversity of these taxa with six species from two different families: Selenoribatidae and Fortuyniidae. Indopacifica, a new genus of Selenoribatidae, is described from Thailand and Malaysia, with two new species, Indopacifica pantai n. sp. and Indopacifica parva n. sp. The genus is characterized by the unique combination of following characters: lacking lamellar ridges, incomplete dorsosejugal suture, fourteen pairs of notogastral setae, and presence of epimeral foveae. A phylogenetic reconstruction based on 18S ribosomal RNA sequences clearly confirms the distinctness of the new genus Indopacifica and places it close to the genus Rhizophobates. The lack of molecular genetic data of possible relatives impedes a clear assessment, and hence, we emphasize the need for further combined approaches using morphological and molecular genetic sequence data. All species show wide distribution areas within this geographic region suggesting that these taxa are good dispersers despite their minute size and wingless body. Molecular genetic data demonstrate recent gene flow between far distant populations of I. pantai n. sp. from the coasts of Thailand and two islands of Malaysia and hence confirm this assumption. The seasonally changing surface currents within this geographic area may favor hydrochorous dispersal and hence genetic exchange. Nevertheless, morphometric data show a slight trend to morphological divergence among the studied populations, whereas this variation is suggested to be a result of genetic drift but also of habitat differences in one population of Alismobates pseudoreticulatus.

A new species of Alloscopus Börner, 1906 (Orchesellidae: Heteromurinae), A. arborealis sp. nov., is herein described from Mt. Makiling, Laguna, Philippines. The new species is distinct from its blind congeners by the combination of: 7+7 macrochaetae on head ‘An’ series and 1+1 on ‘M’ series; 13+13 macrochaetae on thorax II (vs. 9–12) and 7+7 central on thorax III (vs. 6+6); absence of the microsensilla on abdomen I; abdomen IV with four sensilla (vs. three); and ventral tube with a small number of chaetae on its posterior face (4–5 vs. 11–23) and lateral flap (7 vs. 9–16). The complete body chaetotaxic pattern of the new species and a revised key to the world fauna of Alloscopus are also provided.