Redescrição das espécies de sigara fabricius, 1775 (insecta, Heteroptera, corixidae) do estado do Rio Grande do Sul, Brasil e descrição de uma nova espécie de sigara sp.

Abstract

Water boatmen (Corixidae) constitute the largest group of water bugs, with well over 40 species occurring in Brazil. These free-swimming bugs occur in a number of habitats, including running and standing waters, brackish pools, and intertidal ocean waters. They differ from other Nepomorpha because of their feeding habits. They may be classified as herbivore-detritivore, omnivores, predators, or scavengers, depending on the species. Members of Sigara Fabricius are notable as herbivores. Most of the species of Sigara are known from Neotropics, and 11 of them have been reported in Brazil. Since little is known about the distribution and taxonomy of Sigara species of Rio Grande do Sul, there in we the Corixidae species of this state for the first time. The following seven species are recorded and redescribed: Sigara (Tropocorixa) chrostowskii Jaczewski, S. (T.) denseconscripta (Breddin), S. (T.) dita Jaczewski, S. (T.) hungerfordi Jaczewski, S. (T.) platensis Bachmann, S. (T.) schadei (Hungerford), and S. (T.) townsendi (Hungerford). Four new records from this state are reported: S. (T.) dita, S. (T.) hungerfordi, S. (T.) schadei (this species is newly reported in Brazil), and S. (T.) townsendi. A new species is described from Serra Geral Region, northeastern of Rio Grande do Sul state. This species resembles S. (T.) hungerfordi mainly 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 members of such species can be readily recognized by the following aspects of right clasper: presence of a short hook at its apex and serrations along margin of its pre-apical portion. In this new species the right margin of the seventh abdominal segment is not angulated and its median lobe is produced along its left margin, whereas in S. (T.) hungerfordi the right margin of the seventh abdominal segment is strongly pronounced. A key to the species of Sigara occurring in Rio Grande do Sul, as well as the inclusion of a new species, 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 described here.