Descriptions of two new species and a new record of the giant pill-millipede genus Zephronia Gray, 1832 from Thailand (Diplopoda, Sphaerotheriida, Zephroniidae)

Two new species of the millipede genus Zephronia Gray, 1832 are described from Thailand, viz., Z. sukhothaiensis Srimongkol &; Srisonchai sp. nov. and Z. tratensis Srimongkol &; Srisonchai sp. nov., based on an integrative taxonomic approach. The new species can be distinguished from all congeners by a combination of characters, especially the length of the bristles on the endotergum of the midbody tergite and the shape of the telopods. Mitochondrial COI gene divergences between the two new species and the closely related species are more than 11% for Z. sukhothaiensis sp. nov. and 12% for Z. tratensis sp. nov., which supports their recognition as separate species. The species Zephronia ovalis Gray, 1832 is recorded from Thailand for the first time and is redescribed based on newly collected specimens from Sisaket Province. This new record indicates a transboundary distribution for Z. ovalis and highlights the biogeographical connectivity between Thailand and Vietnam. Furthermore, morphological characters of a newly discovered population of Zephronia macula Srisonchai &; Wesener, 2024 are also updated and discussed, and compared to the type material. The variation observed in this newly discovered population reveals an extreme colour plasticity within Z. macula and provides a cautionary example regarding the unreliability of colouration for species delimitation. Morphological illustrations of Z. macula, Z. ovalis, Z. sukhothaiensis sp. nov., Z. tratensis sp. nov., an identification key, and a distribution map of all species of Zephronia occurring in Thailand are also provided.