DNA-barcoding reveals cryptic diversity and re-evaluation of Ocypode (family: Ocypodidae) from the Sundarbans - UNESCO World Heritage Centre

Crabs are one of the most diversified crustaceans among metazoans, from both morphological and ecological point of view. Among them, ghost crabs (Genus Ocypode; Family Ocypodidae) play an important role in the tropical and sub-tropical intertidal ecosystems. Due to a lack of comprehensive data, their cryptic behaviour, mimicry or camouflage, and a lack of formal taxonomic documentation, identification of this group is often difficult. Molecular taxonomy can help to overcome these barriers by assisting in species identification. The present study is the first large scale attempt to identify ghost crabs using DNA barcodes, which are now available globally, for 16 morphospecies in the genus Ocypode. A total of 164 barcodes were analysed for species delimitation that are available globally including specimens collected from the Indian Sundarbans. Various species delimitation methods (K2P, NJ, Bayesian supported PTP and Bayesian tree) revealed a total of 19 MOTUs for 16 distinct species where multiple MOTUs were observed in 3 species with inconsistencies in genetic distances and tree topologies. We recognised cryptic diversity in Ocypode macrocera, O. platytarsis and O. quadrata with intraspecies distances greater than the species delimitation threshold of 0.053 ± 0.01. The current study also concluded that O. platytarsis and O. brevicornis are two distinct species, putting an end to the debate over their species synonymy. Furthermore, our Bayesian analysis confirmed the retraction of the genus Hoplocypode specified only for O. occidentalis. As a result, the current research added a new dimension to ghost crab taxonomy by contributing to the detection of cryptic species, thus speculating the possibility of new species and reaffirming the effectiveness of the DNA barcoding while demanding enrichment of the global database for comprehensive species identification and extensive approach of molecular taxonomy as well as morphological interventions in solving taxonomic puzzles.