The antbirds (Thamnophilidae) are a large family, with over 220 species. Until recently, it was thought that all members of this diverse suite of species were restricted to habitats dominated by one form or another of woody vegetation. Our view of antbirds was changed considerably, however, by the discovery in the 1990s of the Parana Antwren. As suggested by the English name, this species has a very restricted geographic range, centered on the southern Brazilian state of Paraná. This species also is known as the Marsh Antwren, however, because it is entirely restricted to marshes. It primarily is known from littoral marshes, but it also occurs in riverine marshes, wet fields, and in mangrove swamps. Although the Parana Antwren currently is classified in a separate genus, it is similar is size and morphology to antwrens of the genus Formicivora. Little is known about the biology of this species. In the meantime, due to its small geographic range and loss of habitat from human activities, the conservation status of the Parana Antwren is assessed as Endangered.