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AbstractIn this contribution, a new pubescent Trechusspecies for the Iberian Peninsula is described, and the use of some morphological traits in the systematic of Trechini are discussed. Micropubescence is common in endogean and troglobite species which are closely related with the “terrestrial-phreatic habitat”. It probably enhances survival in swampy environments through the retention of air bubbles in immersion conditions and promoting flotation. Neither this trait, anophthalmy nor inner sac of aedeagus without sclerotized pieces can be used to support supraspecific taxa. Thus, we propose the formal synonymy of Hydrotrechuswith Trechus[Hydrotrechussyn. nov. of Trechus]. To avoid secondary homonymy, we propose the name Trechus triamicorumnom. nov. for Hydrotrechus cantabricusCarabajal, García & Rodríguez 1999 [already occupied by Trechus cantabricusJeannel 1927, synonym of Trechus distigmaKiesenwetter 1851]. We also propose the synonymization of the subgenus Trichapoduvaliuswith Apoduvalius[Trichapoduvaliussyn. nov. of Apoduvalius]. The new hypogean species with pubescent elytra, Trechus cifrianaesp. nov., is described. The morphology of the species suggests that it probably inhabits the Mesovoid Shallow Substratum (MSS) or the fissure network (mesocaverns and microcaverns) of the cave where the only individual was found. The structure of internal female genitalia suggests a close relationship between T. cifrianaesp. nov. and T. carrilloiToribio & Rodríguez 1997.

The Diserud–Ødegaard multiple-site similarity index makes use of data on species shared by two or more sites, but produces equal similarity values in two different circumstances: species loss and true species turnover. We developed a new multiple-site similarity measure, which is independent of richness and performs better than the Diserud–Ødegaard index under conditions of equal richness between sites, because it discriminates between situations in which shared species are distributed evenly among sites or concentrated in few pairs of sites. We conducted several simulations to assess the relative performance of both the indices. The use of the new measure is recommended, enabling the simultaneous analysis of turnover and richness gradients based on two independent measures.