Identity of Pelodiscus sinensis revealed by DNA sequences of an approximately 180-year-old type specimen and a taxonomic reappraisal of Pelodiscus species (Testudines: Trionychidae)

Recent studies identified several distinct genetic lineages within the softshell turtle genus Pelodiscus that could represent valid species. Traditionally, Pelodiscus was regarded to comprise only a single species (P. sinensis). These softshell turtles are economically the most important chelonians of the world, with hundreds of millions of specimens traded as food every year. Moreover, Pelodiscus is used as a model organism for embryological and physiological studies, making correct species identification of paramount interest for disciplines beyond taxonomy. However, the understanding of the diversity of Pelodiscus was seriously hampered by the unclear taxonomic allocation of the oldest available species name, Trionyx (Aspidonectes) sinensis Wiegmann, 1834. To clarify its identity, we reconstructed two mitochondrial DNA fragments of 1013 bp (cytb) and 468 bp (ND4) length of one of the two surviving syntypes and designate this specimen as lectotype (ZMB 38, Museum für Naturkunde Berlin). The sequences obtained from the lectotype represent a previously unknown lineage. Using the phylogenetic placement of all lineages and uncorrected p distances of the mitochondrial cytb gene as a yardstick, we suggest that the observed sequence variation is consistent with the existence of at least four distinct species within Pelodiscus. The name P. sinensis should be restricted to turtles harbouring the mitochondrial lineages B, C, D and the lineage of the lectotype. More divergent lineages are to be identified with P. axenaria, P. maackii and P. parviformis, which are recognized as valid species.