The millipede genus Sphaerobelum Verhoeff, 1924, in Thailand, with descriptions of three new species (Diplopoda, Sphaerotheriida, Zephroniidae)

Three new species of the giant pill-millipede genus Sphaerobelum Verhoeff, 1924, from Thailand and Laos, are described based on an integrative approach that combines morphological characters and COI data; these are S. nonghinensis Srikampha & Srisonchai, sp. nov. , S. onyx Srikampha & Srisonchai, sp. nov. , and S. petramurum Srikampha & Srisonchai, sp. nov. Additionally, new material of previously described species, S. aesculus Rosenmejer & Wesener, 2021, S. truncatum Wongthamwanich, 2012, and S. turcosa Srisonchai & Pimvichai, 2023, were collected and examined. The new species can be distinguished from all congeners by a combination of unique characters, including body colour, endotergum, vulva, and details of the telopods. The validity of these new species is further supported by high genetic distances from their congeners in the 658 base pairs of the COI barcoding fragment, ranging from 13.24–30.12%. Preliminary phylogenetic analyses using Bayesian inference and maximum likelihood indicate that each new species forms a distinct clade, supporting their morphological uniqueness, though the interrelationships with most other congeners remain unsupported. All new species are restricted to narrow distribution areas in Thailand and Laos, suggesting they are endemic to these regions. Morphological characters of the new species are illustrated, and an identification key and a distribution map for known Sphaerobelum species in Thailand are also provided.