Revision of the genus Hydrobiomorpha Blackburn, 1888 (Coleoptera, Hydrophilidae) from Argentina, with the description of a new species and an updated identification key Author Urcola, Matías R. 0000-0002-1335-0072 Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento Biodiversidad y Biología Experimental, Laboratorio de Entomología, Buenos Aires, Argentina & CONICET-UBA, Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Buenos Aires, Argentina Author Rodriguez, Georgina 0000-0002-0201-2932 Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento Biodiversidad y Biología Experimental, Laboratorio de Entomología, Buenos Aires, Argentina & CONICET-UBA, Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Buenos Aires, Argentina Author Michat, Mariano C. 0000-0002-1962-7976 Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento Biodiversidad y Biología Experimental, Laboratorio de Entomología, Buenos Aires, Argentina & CONICET-UBA, Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Buenos Aires, Argentina Author Torres, Patricia L. M. 0000-0002-6532-9347 Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento Biodiversidad y Biología Experimental, Laboratorio de Entomología, Buenos Aires, Argentina & CONICET-UBA, Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Buenos Aires, Argentina text ZooKeys 2026 2026-08-11 1289 109 139 journal article 316041 10.3897/zookeys.1289.202453 f122728e-4c3e-42ec-a7d9-1458343f19f0 AA854D31-2E42-4639-B597-A4CA6A67DAFF Hydrobiomorpha utiariti Bachmann, 1988 Figs 5 AC – AF, 9 Hydrobiomorpha utiariti Bachmann, 1988: 8 , 18, 19, fig. 6 A – K (original description). Type locality. Brazil : Mato Grosso Norte , Utiariti , Río Papagaio [ 13°01'38"S , 58°16'57"W ] . Material examined. Brazil : • Mato Grosso , Utiariti , Río Papagaio [ 13°01'38"S , 58°16'57"W ], xi.1966 , JM Viana leg., 1 ♂ ( holotype , MACN -En 2746 ) and 1 ♀ ( allotype of Bachmann 1988 , MACN -En 2747 ) . Paraguay : • Puerto Vallemí [ 22°09'27"S , 57°57'05"W ], 11.vi.1952 , AO Bachmann leg., 1 ♀ ( paratype , MACN -En 2748 ) . Diagnosis. L : 22.0 mm (male holotype ), 21.0– 22.5 mm (females). W : 10.0 mm (male holotype ), 9.4–10.0 mm (females). Body shape (Fig. 9 A, B ): navicular, sides subparallel, slightly expanded at mid-length, moderately convex; elytral margins slightly reflexed, especially posteriorly, more distinctly in males than in females. Prosternal keel (Fig. 9 C ): ventral margin straight, posterior spine very short. Metaventral keel (Fig. 9 C ): slightly broadened, with a fine longitudinal groove; posterior end rounded, reaching middle of first abdominal ventrite. Male: mesotibial setigerous furrow present, ~ 1 / 2 of tibial length, narrow, with a dense brush of reddish setae (Table 1 ); fifth abdominal ventrite with a subtriangular, very large glabrous area, ~ 2 / 3 of its total length (Fig. 9 E ); claws robust; protarsal claws with robust proximal tooth on inner claw; mesotarsal claws with somewhat spatulate proximal tooth; metatarsal claws unknown, not preserved in the holotype (only known male); genitalia: median lobe broad, apex truncate, bearing two slightly divergent projections arising centrally from the margin; accessory appendages of median lobe elongate, strongly sclerotized, abruptly narrowed distally, terminating in short outwardly directed apical hooks; parameres as long as the median lobe, broad in lateral view, strongly curved, with subdistal denticulations and apices directed toward the midline (Fig. 5 AC – AF). Female: fifth abdominal ventrite with subtriangular glabrous area, <1 / 2 of its total length (Fig. 9 F ). Figure 9. A – C. Habitus of Hydrobiomorpha utiariti holotype ( MACN -En 2746 ); A. Dorsal aspect; B. Ventral aspect; C. Lateral aspect; D. Labels of the Hydrobiomorpha utiariti holotype; E. Abdominal ventrites IV – V of Hydrobiomorpha utiariti holotype, ventral aspect; F. Abdominal ventrites IV – V of Hydrobiomorpha utiariti female labelled as allotype ( MACN -En 2747 ), ventral aspect. Scale bars: 5 mm (A – C), 2 mm (E, F). Distribution. Brazil ( Bachmann 1988 ), Paraguay ( Bachmann 1988 ). Biology. Unknown. Remarks. Hydrobiomorpha utiariti is included herein because it overlaps in distribution with H. bachmanni sp. nov. in Paraguay and presents similar anatomical features, particularly in body size, convexity, and development of male mesotibial setigerous furrow and glabrous area of fifth abdominal ventrite, which may lead to confusion between the two species. Hydrobiomorpha utiariti differs from H. bachmanni sp. nov. by its larger size, darker coloration, longer male mesotibial setigerous furrow (~ 1 / 2 of tibial length, whereas in H. bachmanni sp. nov. it extends ~ 1 / 3), and larger glabrous area in both sexes (~ 2 / 3 of its total length in males (Fig. 9 E ) and <1 / 2 in females (Fig. 9 F ), whereas ~ 2 / 5 in both sexes in H. bachmanni sp. nov. (Fig. 4 A, B ). It also differs in the prosternal keel, which is shorter in H. utiariti and bears a short posterior spine, and in the shape of the male genitalia: the median lobe has two slightly divergent apical projections in H. utiariti (Fig. 5 AC – AF), whereas in H. bachmanni sp. nov. these are subparallel (Fig. 5 A – D ); and the parameres of H. utiariti bear conspicuous subdistal internal denticulations that are absent in H. bachmanni sp. nov.