Lepidion lepidion and Lepidion eques are two nominal species of the genus Lepidion (Moridae) from the Mediterranean Sea and the North Atlantic Ocean, respectively. Following the publication of the latter species, several authors highlighted the morphological similarities between them, questioning their taxonomic relationship. Despite these reasonable doubts, the two species have long been considered as valid and separate species. Since the 2010s, a series of integrative studies, combining morphological and molecular analyses, have demonstrated that L. eques is a junior synonym of L. lepidion. However, the former has continued to be used inconsistently in biodiversity databases and ichthyological literature. Thus, while the “Catalog of fishes” immediately incorporated this new status, the databases “FishBase” and “WoRMS” did not, maintaining the validity of both species. Consequently, in the scientific literature, only a few authors adhere to the synonymy relationship, naming the Atlantic species as L. lepidion, while most maintain the older nomenclature of L. eques. These two nominal species represent an interesting case study on the application of taxonomic nomenclature and how the different criteria for incorporating new species affect the scientific community.