Two new species and two new country records of the giant pill-millipede genus Zephronia Gray, 1832 from Thailand, based on integrative taxonomy (Diplopoda, Sphaerotheriida, Zephroniidae)

An integrative taxonomic study combining morphological and molecular data revealed two new species of giant pill-millipedes of the genus Zephronia Gray, 1832: Zephronia tamarindina Wilaisorn & Srisonchai, sp. nov . and Zephronia triforma Wilaisorn & Srisonchai, sp. nov ., both endemic to provinces in the upper central region of Thailand. In addition, Zephronia dawydoffi Attems, 1953 and Zephronia laotica Wesener, 2019 are recorded from Thailand for the first time. The new species exhibit distinctive colouration patterns, and scanning electron microscopy revealed unique morphological characters for each taxon. Analysis of the 658 bp DNA barcoding region of the mitochondrial COI gene showed interspecific genetic distances ranging from 8.68–21.92% for Z. dawydoffi , 12.79–22.98% for Z. laotica , 10.81–22.07% for Z. tamarindina sp. nov ., and 10.81–22.83% for Z. triforma sp. nov ., in comparison with closely related species from Thailand, Vietnam, Laos, and Cambodia. Phylogenetic analyses placed all four species within the Zephronia s.s. clade, characterised by the Tömösváry’s organ located outside the antennal groove. However, relationships among other clades remained unresolved due to interspersion with species of Cryxus Leach, 1814, Prionobelum Verhoeff, 1924, and Sphaerobelum Verhoeff, 1924. Zephronia was recovered as non-monophyletic, indicating that the current generic limits within Zephroniinae require reassessment using multi-locus data. These results expand our understanding of giant pill-millipede diversity and highlight the upper central Thai region and Southeast Asia more broadly as a significant biodiversity hotspot.