Online biogeographic databases are increasingly being used as data sources for scientific papers and reports, for example, to characterize global patterns and predictors of marine biodiversity and to identify areas of ecological significance in the open oceans and deep seas. However, the utility of such databases is entirely dependent on the quality of the data they contain. We present a case study that evaluated online biogeographic information available for a hydrozoan narcomedusan jellyfish, Aegina citrea. This medusa is considered one of the easiest to identify because it is one of very few species with only four large tentacles protruding from midway up the exumbrella and it is the only recognized species in its genus. Online resources such as the Global Biodiversity Information Facility (GBIF) and the Ocean Biogeographic Information System (OBIS) suggest that A. citrea is broadly distributed throughout the world's oceans. However, lack of traceability to information from original providers made it impossible to validate the great majority of records in online resources, casting doubt on species identification. Thus, we conducted a new systematic investigation of A. citrea, integrating morphological and genetic observations of specimens obtained from a variety of different localities. Contrary to the status quo, our molecular phylogenetic analysis shows that the genus Aegina and the family Aeginidae are polyphyletic. In conjunction with our phylogenetic framework, we clarify the morphological characters distinguishing different clades of 'Aegina'. To accommodate for the previously unrecognized diversity in this group, we describe two new families, three new genera, and one new species. In addition, we clarify the identities of found species by providing updated descriptions. Specifically, we redescribe A. citrea, and resurrect and redescribe A. rosea, A. brunnea (as Aeginona brunnea gen. nov.), A. rhodina and A. pentanema, erecting a new family and genus for the latter two species (Pseudaeginidae, Pseudaegina). A new genus and species, Solmundaegina nematophora, is also described, with the erection of a new family Solmundaeginidae to contain it and the genera Solmundella, Aeginopsis and Solmundus. In light of our integrative systematic study, we find that many past conclusions about the biology of 'Aegina citrea', from life history to ecology to distributions, are compromised because observations of more than one species were applied to a single name, highlighting how systematics and taxonomy provide the foundation upon which all other biological science is built.http://zoobank.org/urn:lsid:zoobank.org:pub:AF6B533C-8110-44A0-A7E5-B71F878DAC4A
