Phylogenetic studies of Aleocharinae rove beetles, arguably one of the least known and the largest insect lineages, are compromised by its enormous taxonomic diversity. DNA, a powerful resource for phylogenetics, is not available for numerous extant aleocharine species. We provide a broad comparative morphological study of Aleocharinae to frame molecular datasets for total-evidence analyses. Using full-body dissections and slide-mounting techniques for light microscopy supplemented by scanning electron microscopy, we constructed a morphological matrix across all major taxa focused on non-inquiline tribes of Aleocharinae and outgroups. Phylogenetic analyses of this matrix concatenated with earlier published DNA loci and including exemplar taxa lacking molecular data, resolved outstanding controversies and, among other novelties, showed that: the Habrocerinae + Trichophyinae clade is sister group to Aleocharinae; Hypocyphtini are sister to the rest of the "higher Aleocharinae"; Taxicerini are sister to Aleocharini; Hoplandriini and Placusini are nested within a polyphyletic Oxypodini; Hoplandriini are sister to Meoticina; and Actocharini are nested within Liparocephalini. For the first time, morphological synapomorphies are identified for some large clades of Aleocharinae. In addition, 1252 high-resolution microphotographs of aleocharine structures are made available online with the entire matrix for future research.

Insects have invaded marine habitats only rarely and secondarily. Recently, we discovered a flightless dipteran species skating rapidly on the surface of seawater ponds at the Pacific coast of eastern China. Morphological analyses initially suggested an isolated position of the non‐biting midge, suggesting the erection of a new genus within Chironomini (Diptera: Chironomidae). However, an analysis of molecular data revealed that the marine species is in fact nested within the species‐rich genus Dicrotendipes. The apparent conflict between molecular and morphological data can be easily explained. It is likely that the new species has evolved a series of autapomorphic adaptations. These traits clearly distinguish the taxon from other species of the genus but do not justify the erection of a new supraspecific taxon, which would render Dicrotendipes paraphyletic. The switch to marine environments was likely a trigger for various morphological modifications resulting from increased selective pressure. Molecular data suggest that the potential speciation event occurred around 19–29 Ma, linked with a migration from freshwater to seawater ponds along the Pacific Ocean. Considering the results of our analysis, we place the flightless marine skater in the genus Dicrotendipes. All life stages of Dicrotendipes sinicus Qi & Lin sp. n. are described and illustrated, associated with larvae obtained by rearing or confirmed through association with DNA barcodes. The biology and ecology of the species are outlined based on collection data and in situ observations. Evolutionary patterns linked with repeated invasions of marine habitats are discussed.