Revision of the genus Hydrobiomorpha Blackburn, 1888 (Coleoptera, Hydrophilidae) from Argentina, with the description of a new species and an updated identification key.

The genus Hydrobiomorpha Blackburn, 1888 is a pantropical group of aquatic beetles that play important roles in freshwater ecosystems as predators (larvae) and scavengers (adults). In South America, 31 species are known, with six previously recorded from Argentina: Hydrobiomorpha corumbaensis Mouchamps, 1959, H. iguazu Bachmann, 1988, H. irina irina (Brullé, 1837), H. longa (Bruch, 1915), H. rudesculpta (Orchymont, 1939) and H. spinosa (Orchymont, 1928). Building on the foundational contributions of Dr. Axel O. Bachmann to the taxonomy of the genus in the Americas, a comprehensive revision of the Argentine species of Hydrobiomorpha is presented, integrating high-resolution digital photography and scanning electron microscopy to document anatomical features in detail. Seven species are recognized, including H. bachmanni sp. nov., described from Argentina (Corrientes Province) and Paraguay, dedicated to Dr. Bachmann in recognition of his legacy. For comparative purposes, H. utiariti Bachmann, 1988 is also treated, given its anatomical similarity to the new species. An updated identification key to the Argentinean species is provided. The presence, extent, and location of the male mesotibial setigerous furrow, claw structure, the glabrous area on the last abdominal ventrite, and male genitalia are evaluated as key diagnostic characters, revealing consistent interspecific variation. Distribution patterns show highest species richness in northeastern Argentina, with H. spinosa (Orchymont, 1928) exhibiting the broadest range and H. iguazu Bachmann, 1988 restricted to Misiones Province. This revision provides a modern, visually documented taxonomic framework that facilitates accurate species identification for future phylogenetic, ecological, and conservation studies.