Integrative taxonomy reveals two new giant pill-millipedes from Thailand

A large amount of material of the millipede genus Zephronia Gray, 1832 was collected during 2014–2023 from many parts of eastern Thailand. An integrative study of morphological characters and genetic data (COI gene) revealed two new species: Z. chantaburiensis Srisonchai & Wesener, sp. nov. and Z. macula Srisonchai & Wesener, sp. nov. The two new species clearly differ from other congeners by their unique characteristics, especially in their colour pattern and telopod shape. The interspecific genetic distances of the 658 bp COI gene barcoding fragment between these new species and all other species of giant pillmillipede from Thailand, Laos and Cambodia are 12.01–23.49% for Z. chantaburiensis sp. nov. and 17.93–25.13% for Z. macula sp. nov. While relationships among species remain preliminary, the phylogenetic tree shows that species of Zephronia are interspersed with species of Sphaerobelum Verhoeff, 1924 and Prionobelum Verhoeff, 1924. Phylogenetic analyses place both new species in a clade termed Zephronia s.s., which receives support also from morphological data, showing a unique position of the organ of Tömösváry. Z. macula sp. nov. appears to occur over a broad distribution whereas Z. chantaburiensis sp. nov. was found only at the type locality. Given that all known records are in the eastern part of Thailand, we thus regard both species as endemic. Morphological illustrations based on SEM micrographs and a distribution map are also provided.