Mouthpart structure of Stylogymnusa subantarctica Hammond, 1975 (Coleoptera: Staphylinidae: Aleocharinae) with a reanalysis of the phylogenetic position of the genus

Structure, particularly of the mouthparts, of the unusual aleocharine staphylinid Stylogymnusa subantarctica Hammond was reevaluated. The mouthparts are described in detail, and drawings of their structure are provided. Several features were found to be misinterpreted in previous accounts of the structure of this aleocharine. In particular, the stylate structures found on the prementum are not a highly modified, hollow, stylate glossa, as had been previously suggested. Instead, these structures represent highly modified labial palpi; the segments are completely fused, all signs of typical setae of the labial palpi are missing, and the palpi are very long and slender. In addition, there is no sign that they are hollow. Small, slender, membranous lobes at the base of, and between, the palpi are interpreted as the true glossae (= ligula). Reinterpretation of these characters, and greatly improved phylogenetic techniques in the 20 years since previous phylogenies had been proposed, allowed testing of previous hypotheses of the phylogenetic position of Stylogymnusa and the relationships of the tribes Gymnusini and Deinopsini within the Aleocharinae. Phylogenetic analysis of 7 out-group and 12 in-group taxa, based on 84 characters and 231 character states, produced 3 equally most-parsimonious trees (tree length=253, C.I.=0.557, R.I.=0.674, rescaled C.I.=0.376). These trees provide strong support for a monophyletic lineage consisting ofStylogymnusa , Gymnusa and the Deinopsini but only weak support for a monophyletic Gymnusini (Gymnusa+Stylogymnusa). Bootstrap analysis based on 1000 resampling repetitions showed the following monophyletic clades to be well supported by the dataset: Aleocharinae (79%),Stylogymnusa +Gymnusa+ Deinopsini (99%), Deinopsis+Adinopsis (100%), and representatives of Myllaenini + Athetini + Aleocharini + Homalotini + Oxypodini (the “higher Aleocharinae”) (88%). Weakly supported clades in the bootstrap analysis were Paraconosoma+ Gymnusini + Deinopsini (56%), Anacyptus+ «higher Aleocharinae» (54%), and Athetini + Oxypodini + Homalotini + Aleocharini (52%).