Combining mitochondrial DNA and morphological data to delineate four new millipede species and provisional assignment to the genus Apeuthes Hoffman & Keeton (Diplopoda : Spirobolida : Pachybolidae : Trigoniulinae)

Hitherto, the millipede genus Apeuthes (family Pachybolidae, subfamily Trigoniulinae) was only known from three species described in Vietnam based on morphological characters. The present study uses two partial mitochondrial gene fragments (cytochrome c oxidase I (COI) and 16S ribosomal RNA) and morphology to define four new Apeuthes species from Malaysia, Thailand and Vietnam: A. fimbriatus, sp. nov., A. longeligulatus, sp. nov., A. pollex, sp. nov. and ?A. spininavis, sp. nov. The intraspecific COI sequence divergence of two Apeuthes species is 3–7% (mean: 5%) and the interspecific divergence of five species is 11–16% (mean: 13.7%). All members of the genus share unique male characters, viz the posterior gonopod telopodite with several dentate, serrate or tuberculate lamellae in a boat-like cavity or a boat-like cavity covered with spines. The delimitation of the four new species is supported by the congruence between mitochondrial DNA and morphological data. However, while the monophyly of Trigoniulinae is well supported, the relationships within this subfamily, and particularly among Apeuthes species, including the monophyly of Apeuthes, lack strong support. Therefore assignment of the four new species, and particularly of ?A. spininavis sp. nov., to the genus Apeuthes is tentative and awaits a comprehensive revision of the group.