Seven species of Didymozoidae were found parasitizing three species of scombrid fishes along the Rio de Janeiro coast, southwestern Atlantic Ocean. All these species are reported here for the first time in Brazil and new hosts are presented, which adds to the knowledge of these species. The main morphological and morphometric features of each species are presented. A new combination of two species allocated to Lobatocystis Yamaguti, 1965 is proposed here, based on the previously established synonymy of Lobatocystis and Lobatozoum Ishii, 1935.