Among several other cases of taxonomic indefinition within the cyclopoid copepod genus Mesocyclops, we selected and examined in detail two neotropical species with overlapping distributional ranges: M. meridianus (Kiefer, 1926) and M. brasilianus Kiefer, 1933. The latter has long been considered as a synonym of M. meridianus by some authors, while other specialists recognize both forms as valid. The available descriptions were not detailed enough to determine the taxonomic status of the two. Upgraded descriptive standards, including SEM analysis, were used in order to provide morphological data for both species, emphasizing microcharacters. After examination and comparison of both male and female specimens collected in several neotropical areas (Mexico, Peru, Brazil, Venezuela), we confirmed that M. brasilianus and M. meridianus are in fact valid, separate taxa. This statement was based on previously undetected differences in the ornamentation of the antennules, antennal basis, maxillulae, maxillae, and swimming legs 3 and 4, among other structures. A detailed complementary description and depiction of both species is provided herein. Males of both species are described in full for the first time. This kind of analysis is expected to mark new standards and to become a major tool in re-defining the species limits of the neotropical Mesocyclops.