Accurate species identification underpins all biological research, conservation, and resource management. Assigning correct names to specimens enables access to existing knowledge on their habitat, distribution, and genetic data; however, this is only reliable when prior identifications are correct. Errors in identification can propagate through databases such as GenBank, particularly when sequences are not linked to specimens from type localities or when voucher material is absent. Such inaccuracies may lead to flawed conclusions, including misleading phylogenies or incorrect interpretations of reproductive biology, ultimately resulting in wasted time, effort, and financial resources. The issue is especially evident in polychaetes, where many species have historically been considered “cosmopolitan,” occurring across broad geographic regions. Integrative approaches combining molecular and morphological analyses increasingly reveal that these presumed widely distributed species are, in fact, complexes of multiple distinct species. For instance, Marphysa sanguinea, originally described from the United Kingdom, was long reported in Australia; it is now recognized that at least eight species of this genus occur. Misidentification has practical consequences, as fisheries often manage these organisms as a single species despite significant differences in their reproductive strategies. Another example is distinguishing between native and introduced species or how different species respond to climate change.