A taxonomic revision of South American species of the genus Stenostomum O. Schmidt (Platyhelminthes: Catenulida) based on morphological characters

This paper revises the genus <i>Stenostomum</i> based on a rich collection of species from Argentina and on a review of bibliographical resources of all known South American species. The description of South American species is standardized. The new genus <i>Anokkostenostomum</i> is established and several species of <i>Stenostomum</i> are transferred to it based on the absence of light-refracting bodies and the presence of a metameric anterior brain lobe. We report five <i>Stenostomum</i> species and three <i>Anokkostenostomum</i> species new to Argentina and present an identification key for South American species. Finally, all the world species are compiled, with an overview of their distribution.