The origin and early evolutionary history of polyphagan beetles have been largely based on evidence from the derived and diverse ‘core Polyphaga’, whereas little is known about the species-poor basal polyphagan lineages, which include Scirtoidea (Clambidae, Decliniidae, Eucinetidae, and Scirtidae) and Derodontidae. Here, we report two new species Acalyptomerus thayerae sp. nov. and Sphaerothorax uenoi sp. nov., both belonging to extant genera of Clambidae, from mid-Cretaceous Burmese amber. Acalyptomerus thayerae has a close affinity to A. herbertfranzi , a species currently occurring in Mesoamerica and northern South America. Sphaerothorax uenoi is closely related to extant species of Sphaerothorax , which are usually collected in forests of Nothofagus of Australia, Chile, and New Zealand. The discovery of two Cretaceous species from northern Myanmar indicates that both genera had lengthy evolutionary histories, originated at least by the earliest Cenomanian, and were probably more widespread than at present. Remarkable morphological similarities between fossil and living species suggest that both genera changed little over long periods of geological time. The long-term persistence of similar mesic microhabitats such as leaf litter may account for the 99 Myr morphological stasis in Acalyptomerus and Sphaerothorax . Additionally, the extinct staphylinoid family Ptismidae is proposed as a new synonym of Clambidae, and its only included species Ptisma zasukhae is placed as incertae sedis within Clambidae.

The taxonomic knowledge of the pselaphine tribe Batrisini (Coleoptera: Staphylinidae) from the Tibet Autonomous Region is summarized, with 80 species placed in 13 genera. Two genera and 68 species are described as new, aided with illustrations of habitus and diagnostic characters: Arthromelodes alpitorus sp. nov., A. angulatus sp. nov., A. aniqiao sp. nov., A. bicolor sp. nov., A. complexus sp. nov., A. cona sp. nov., A. crassicornis sp. nov., A. criniger sp. nov., A. cylindricus sp. nov., A. flosculus sp. nov., A. gyamda sp. nov., A. intricatus sp. nov., A. lage sp. nov., A. langjicuo sp. nov., A. latithorax sp. nov., A. lebus sp. nov., A. lotus sp. nov., A. markam sp. nov., A. monba sp. nov., A. nepaeformis sp. nov., A. nomurai sp. nov., A. songxiaobini sp. nov., A. speciosus sp. nov., A. torus sp. nov., A. zhangmu sp. nov., A. zhentangensis sp. nov., Batriscenaulax campestris sp. nov., Batrisiella acclivis sp. nov., Batrisiella beibeng sp. nov., Batrisiella bomea sp. nov., Batrisiella concisa sp. nov., Batrisiella curvitibialis sp. nov., Batrisiella ganma sp. nov., Batrisiella guttata sp. nov., Batrisiella zhujianqingi sp. nov., Batrisodes guoguotang sp. nov., Batrisodes hanmi sp. nov., Coryphomimus levigatus gen. et sp. nov., Coryphomodes budda sp. nov., Coryphomodes cephalicus sp. nov., Coryphomodes chenzhilini sp. nov., Gyrongita uniformis gen. et sp. nov., Sathytes aequalis sp. nov., S. asura sp. nov., S. caichenyangi sp. nov., S. dawai sp. nov., S. duojii sp. nov., S. laticornis sp. nov., S. pengzhongi sp. nov., S. proclivis sp. nov., S. pseudograndis sp. nov., S. sympatricus sp. nov., S. virupaksa sp. nov., S. yigongensis sp. nov., Tribasodites bari sp. nov., T. cellulanus sp. nov., T. constrictus sp. nov., T. dilophus sp. nov., T. elongatus sp. nov., T. grandiceps sp. nov., T. gyirong sp. nov., T. kiypu sp. nov., T. mirabilis sp. nov., T. prolixicornis sp. nov., T. pugiunculus sp. nov., T. vertexalis sp. nov., T. yatung sp. nov., and Trisinus quadrilobus sp. nov. The genus Plocamarthrus Jeannel, 1960 is proposed as a subjective junior synonym of Arthromelodes Jeannel 1954, syn. nov., resulting in Arthromelodes championi (Jeannel, 1960) comb. nov. (type species of Plocamarthrus), A. cameroni (Jeannel, 1960) comb. nov., A. planiceps (Jeannel, 1960) comb. nov., and A. abdominalis (Jeannel, 1960) comb. nov. Arthromelodes championi and Sathytes simplex Löbl, 1979 are reported to occur in Tibet, which are also new country records for China. Additional collecting data are provided for Hingstoniella lata Jeannel, 1960, Sathytes panzhaohuii Yin & Shen, 2020, Sathytes transversus Yin & Shen, 2020, and Sathytes xizangensis Yin & Shen, 2020. Keys for identification of the genera and species are presented. Maps showing the distribution of each species are provided, supplemented with habitat photos. Lists of Tibetan species of Batrisini and of other pselaphine groups are given, adding up to 95 species.

A new species of Pseudophanias Raffray from a cave in central Nepal (Coleoptera: Staphylinidae: Pselaphinae)

The monotypic genus Chandleriella Hlaváč, 2000 is reported from China for the first time, and a new species, C. yunnanica Yin, sp. nov. (type locality: Lincang, Yunnan), is described. It can be readily separated from C. termitophila (Bryant, 1915) of Sarawak by possessing a conspicuously modified antennomere 11 of the male.

Structural colours, nature's most pure and intense colours, originate when light is scattered via nanoscale modulations of the refractive index. Original colours in fossils illuminate the ecological interactions among extinct organisms and functional evolution of colours. Here, we report multiple examples of vivid metallic colours in diverse insects from mid-Cretaceous amber. Scanning and transmission electron microscopy revealed a smooth outer surface and five alternating electron-dense and electron-lucent layers in the epicuticle of a fossil wasp, suggesting that multilayer reflectors, the most common biophotonic nanostructure in animals and even plants, are responsible for the exceptional preservation of colour in amber fossils. Based on theoretical modelling of the reflectance spectra, a reflective peak of wavelength of 514 nm was calculated, corresponding to the bluish-green colour observed under white light. The green to blue structural colours in fossil wasps, beetles and a fly most likely functioned as camouflage, although other functions such as thermoregulation cannot be ruled out. This discovery not only provides critical evidence of evolution of structural colours in arthropods, but also sheds light on the preservation potential of nanostructures of ancient animals through geological time.

The Oriental pselaphine genus Horniella Raffray, 1905 currently contains 29 species. In this paper, six new species are described: H. nantouensis Zhang, Hu & Yin, sp. nov. and H. taiwanensis Zhang, Hu & Yin, sp. nov. from Taiwan, China; H. bifurca Zhang & Yin, sp. nov. and H. haucki Zhang & Yin, sp. nov. from Thailand; H. khasiensis Zhang & Yin, sp. nov. from northern India; and H. sabahensis Zhang & Yin, sp. nov. from eastern Malaysia. In addition, H. aculeata Yin & Li, 2015, originally described from Yunnan, China, is newly recorded from Thailand.