The gondwanic genus Metania GRAY, 1867 of freshwater sponges is redefined in this, the third paper of a series concerned with a revision of the Neotropical species of this genus. Newly detected characteristica indicate a relationship between Metania and the marine genus Acarnus GRAY, 1867 of poecilosclerid sponges. Characteristica similar to those in Metania were also detected in the genera Corvomeyenia WELTNER, 1913, Acalle GRAY, 1867 and Drulia GRAY, 1867. The genera Metania, Corvomeyenia, Acalle, and Drulia are transferred from the family Spongillidae GRAY, 1867 into the new family Metaniidae, based upon an initial analysis of their shared characteristics