Integrative Taxonomy of a New Thyropygus Pocock, 1894 Species from Thailand (Diplopoda: Spirostreptida: Harpagophoridae)

A new juliformian millipede species, Thyropygus sirindhornae sp. nov., is described from Chiang Rai Province, Thailand and assigned to the Thyropygus allevatus group based on two diagnostic gonopodal characters: (1) the gonopod telopodite with both tibial and femoral spines, and (2) a notably long tibial spine recurved toward the femoral spine. Despite its affiliation with the informal T. allevatus group, T. sirindhornae sp. nov. cannot be assigned to one of the four informal subgroups of the T. allevatus group because it lacks any of the diagnostic characters of these subgroups. Similarly, while the COI DNA barcode data support the distinctiveness of T. sirindhornae sp. nov. from other Thyropygus species within the T. allevatus group (mean interspecific sequence divergence of 0.16 ± 0.02, range: 0.12–0.19), they do not provide information about the sister group relationships or subgroup assignment of the new species. As a result, T. sirindhornae sp. nov. is tentatively assigned to the T. allevatus group, but is labelled as “incertae sedis” with respect to its sister group relations and subgroup classification. In fact, as the COI phylogeny only included species of the T. allevatus group, the assignment of T. sirindhornae sp. nov. to this informal species group needs to be confirmed by including representatives of other informal Thyropygus species groups.