A new micropolydesmoid millipede of the genus Eutrichodesmus Silvestri, 1910 from Cambodia, with a key to species in mainland Southeast Asia (Diplopoda, Polydesmida, Haplodesmidae).

The micropolydesmoid millipede family Haplodesmidae is here recorded from Cambodia for the first time through the discovery of the first, new species of the genus Eutrichodesmus Silvestri, 1910: E. cambodiensis sp. nov. This new species is described from two limestone habitats in Kampot Province, based on abundant material. It is easily distinguished from all related congeners by the following combination of characters: body greyish-brown; limbus roundly lobulate; solenomere partially divided from acropodite by a digitiform lobe, but without hairpad. Brief remarks on the previously-proposed "pecularis-group" are provided and a second group, the "demangei-group", is established and discussed on the basis of morphological evidence, updating the number of recognised species groups of Eutrichodesmus to two. Detailed morphological illustrations, photographs and a distribution map, as well as remarks on its habitat and mating behaviour of the new species are presented. Furthermore, the current distributions of all 55 presently-known species of Eutrichodesmus are provided and a key to all 23 species that occur in mainland Southeast Asia is given.