The Curvosa Group comprises three species: H. curvosa (Brazil, Peru), H. takutu (Guyana), and H. hintoni (Brazil). These are rather convex species, moderately sized (ca. 1.48–1.76 mm), with a characteristic habitus (Figs. 16– 18). The coxae are rather widely separated by P 1 and especially P 2, and the plaques are also widely separated. The genae usually have an ill-defined posterior ridge laterally. The male genitalia are quite stout, and have a basic plan similarity; the parameres are moderately large, and the right paramere has modified setae (Figs. 15, 19, 20). The female gonocoxite is "divided", having a weakly sclerotized midlongitudinal area, and is similarly shaped in all species in this group (e.g., Fig. 149). The spermatheca (Figs. 151–152) is circular, somewhat disc-shaped, markedly differing from that of all American Hydraena, except members of the Paeminosa Group. Externally and male genitalically the two groups are very different.
Two of the species in this group, H. curvosa and H. takutu, so far have only been collected from leaf packs taken from streams.