A new species of Hydraena (Coleoptera: Hydraenidae) of the H. evanescens complex from Sardinia*

A morphological analysis was performed in order to clarify the taxonomic scenario within the Hydraena evanescens complex (Coleoptera: Hydraenidae: Hydraeninae), including species associated with fast running waters in mountain areas of Corsica and Sardinia. The analysis was mainly focused on the specific distinction and formal description of a new species, H. rosannae sp. nov., from the Sulcis-Iglesiente region (SW Sardinia), morphologically distinctly separated from both the nearly parapatric H. tyrrhena Binaghi, 1961 (central and northern Sardinia) and the allopatric H. evanescens Rey, 1884 (Corsica). Two hypothetical palaeogeographical scenarios explaining the specific differentiation of the three species are briefly discussed.