Trace-DNA from a century-old holotype specimen resolves taxonomic uncertainties: the case of the Hawaiian pink precious coral ( Pleurocorallium secundum ), a CITES-listed species used in jewelry

The holotype specimen holds the most authentic characteristics of a species; its features will serve as a foundation for the identification of individuals belonging to this species. The precious coral Pleurocorallium secundum was described in 1846 based on a colony from the Hawaiian Islands. This specimen has been preserved; however, it is decorticated and contains exclusively the axial skeleton, which has hindered its use for accurate species identification. Therefore, the species was redescribed in 1956 based on a specimen lot collected in 1902. Pleurocorallium secundum was considered the most frequently fished precious coral species in the second half of the 20 ^th century with landings on the scale of thousands of tons, which was followed by its listing on CITES Appendix III. Recently, the conspecificity of the holotype and the redescribed colonies was questioned and specimens labeled in the scientific literature as P. secundum were discovered to be phylogenetically distant from each other. To clarify the identity of P. secundum , we took minimally destructive samples from the century-old holotype and the redescribed colonies and applied techniques conforming to low copy number DNA analyses. DNA sequences of three mitochondrial regions were evaluated in a phylogenetic framework together with DNA sequences retrieved from freshly collected putative P. secundum specimens and sequences from the scientific literature. The results of this study clearly indicate that the holotype and the redescribed colonies of P. secundum represent the same species. Based on the specimens confirmed to be P. secundum with genetic evidence, the distribution area of P. secundum stretches from the Hawaiian Islands to the South China Sea. At the same time, our analysis uncovered both published and fresh specimens that are in fact not P. secundum . The latter includes the fished Makapuu coral bed in Hawaii, which used to be a significant coral fishing area. Based on the microscopic analysis of the redescribed colonies, we complement the diagnosis of P. secundum . This, together with our genetic results will aid the identification of coral objects present in the international jewelry trade by providing authentic molecular barcoding markers and morphologic features for the identification of P. secundum .