a new species of sigara fabricius (hemiptera, heteroptera, corixidae) and redescription of the species recorded in the state of rio grande do sul, brazil. water boatmen (corixidae) constitute the largest group of water bugs, with well over 40 species occurring in brazil. most of the species of sigara are known from the neotropics, and 11 of them have been reported in brazil. little is known about the distribution and taxonomy of sigara species of rio grande do sul. the following seven species are recorded and redescribed: sigara (tropocorixa) chrostowskii, s. (t.) denseconscripta, s. (t.) dita, s. (t.) hungerfordi, s. (t.) platensis, s. (t.) schadei, and s. (t.) townsendi. sigara (t.) dita, s. (t.) hungerfordi, and s. (t.) townsendi are newly recorded from this state, while s. (t.) schadei is recorded for the first time from brazil. sigara (t.) bachmanni, sp. nov. is described from northeastern rio grande do sul. this species resembles s. (t.) hungerfordi in having the synthlipsis less than 0.9 times the width of an eye, metaxyphus broader than long, and the infraocular portion of genae slender, but can be readily recognized by the presence of a short hook at apex of right clasper and serrations along the margin of its pre-apical portion. a key to the species of sigara occurring in rio grande do sul is provided. although the general aspect of right clasper and the number of pegs of male pala as well as its shape have proven useful for species delimitation, s. (t.) chrostowskii and s. (t.) townsendi have shown considerable variation in these features and have been redescribed here.