| Summary: | Haplotaxis Hoffmeister, 1843 is a poorly known genus: it is rarely collected because it usually inhabits groundwater, and many species are only known from immature specimens. Even the type species, Haplotaxis gordioides (Hartmann in Oken, 1819) remains poorly defined because of the absence of reference types. Most of the Haplotaxis species have been placed in synonymy with H. gordioides since the end of the 19 th century, a situation that has remained essentially unchanged until now. As a result, the species is supposedly present on all continents, except Antarctica. This observation is all the more questionable as the aquatic subterranean environment is nowadays well known to harbour many species with restricted distribution, due to the strong hydrogeographic isolation and the low dispersal abilities of its inhabitants. In this study we assessed the hypothesis of H. gordioides as a single species with wide distribution versus a complex of cryptic species with narrow distribution. We used a DNA-barcoding approach based on the COI mitochondrial marker of 46 Haplotaxis specimens collected in Switzerland, mostly as part of a countrywide sampling campaign to study groundwater macroinvertebrates. Preliminary results suggested that H. gordioides is a complex of at least 6 cryptic species in Switzerland, which has important implications both for the knowledge of the exact identity of the type species and for the synonymy of most of the species described in the 19 th century. However, as it is based on a single-locus approach, this study should be seen as the first step in an integrative taxonomic process that should include additional biological material, the study of complementary markers (especially nuclear), and the morphological study of specimens.
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