Type specimen matters: Authorship, validity and neotypification of the Atlantic yellowfin mojarra Gerres cinereus (Teleostei: Gerreidae).

The Atlantic yellowfin mojarra Gerres cinereus was described from a 1734 illustration by Mark Catesby. Thenceforth, the genus has had a controversial taxonomic history in the Americas. Even though it was once considered monotypic, and its description was not scientifically amended until the end of the 19th century, no type material exists. Catesby's illustration historically has been related to at least five nominal species of Gerreidae, four currently recognised as valid. Our critical examination of Catesby's drawing, the review of historical taxonomic criteria to identify species and the geometric morphometric analysis performed showed that it does not correspond to G. cinereus sensu stricto. Hence, applying the rules of the International Code of Zoological Nomenclature, the binomen could be considered a 'nomen dubium'. However, using a newer synonym would threaten nomenclatural stability and universality because of the name's prevailing usage. Otherwise, conserving the current binomen's usage requires the formal designation of a neotype. On this basis, we designate a neotype for G. cinereus. Although naming species without preserved specimens has never been forbidden, we argue against naming taxa based on unverifiable evidence because the type specimen matters.