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.

Amphipod crustaceans comprise a significant and enigmatic component of Australian groundwater ecosystems, particularly in the Pilbara region of Western Australia. Many amphipod species in the Pilbara, including species in the genus Nedsia Barnard & Williams, 1995, are considered short range endemics, poorly or contentiously defined by taxonomic treatments based on morphology alone and have uncertain distributions as a consequence of this taxonomy. A modern systematic revision of Nedsia is presented here, utilising both molecular and morphological analyses alongside distributional data to delineate species. We describe 13 new species of Nedsia, confirm three existing species and synonymise eight previously described species. Nedsia species are confirmed to be functionally morphologically cryptic, with COI divergences at the 5–20% level. We present comparatively reduced taxonomic descriptions for these cryptic amphipod species in an effort to provide an accelerated pathway for future taxonomic work. The research provides the basis for future environmental impact assessments involving Nedsia species and ongoing monitoring of the groundwater communities these form part of in the resource-rich Pilbara region.

Accurate species delimitation is crucial for our understanding of evolution, biodiversity and conservation. However, morphology-based species delimitation alone appears to be prone to taxonomic errors and ineffective for taxa with high interspecific morphological homogeneity or intraspecific morphological variations, as is the case for mesothele and mygalomorph spiders. Combined molecular–morphology species delimitation has shown great potential to delimit species boundaries in such ancient lineages. In the present study, molecular and morphological evidence were integrated to delimit species of the primitively segmented spider genus Songthela Ono, 2000. The cytochrome c oxidase subunit I gene (COI) was sequenced for 192 novel specimens belonging to 12 putative morphospecies. The evolutionary relationships within Songthela and the 12-morphospecies hypothesis were tested in two steps – species discovery and species validation – using four single-locus species delimitation approaches. All species delimitation analyses supported the 12-species hypothesis. Phylogenetic analyses yielded three major clades in Songthela, which are consistent with morphology. Accordingly, we assigned 19 known and 11 new species (S. aokoulong, sp. nov., S. bispina, sp. nov., S. dapo, sp. nov., S. huayanxi, sp. nov., S. lianhe, sp. nov., S. lingshang, sp. nov., S. multidentata, sp. nov., S. tianmen, sp. nov., S. unispina, sp. nov., S. xiujian, sp. nov., S. zizhu, sp. nov.) of Songthela to three species-groups: the bispina-group, the multidentata-group and the unispina-group. Another new species, S. zimugang, sp. nov., is not included in any species groups, but forms a sister lineage to the bispina- and unispina-groups. These results elucidate a high species diversity of Songthela in a small area and demonstrate that integrating morphology with COI-based species delimitation is fast and cost-effective in delimiting species boundaries.