Historical biogeography of the genus Polycopissa (Ostracoda: Myodocopa: Cladocopina), with the description and DNA barcode of the second Indo-Pacific species from the Seto Inland Sea

A new cladocopid ostracod species, Polycopissa okadai n. sp., is described from the marine interstitial environment of the Seto Inland Sea, western Japan. This is the second representative of this genus identified from the Indo-Pacific region. A detailed morphological observation of the carapace and appendage was performed using a scanning electron microscope. In particular, the results showed that the morphology of the pore system on the outer surface of the carapace could be utilised for generic-level identification and for taxonomic classification of fossil species. In addition, the DNA barcode sequence of this new species was also determined, which was the first such determination within the suborder Cladocopina. Species belonging to Polycopissa Chavtur 1981 show a transoceanic distribution and have been reported from cryptic habitats such as interstitial waters or anchialine caves. The historical biogeography of Polycopissa is the subject of this study, based on previously suggested hypotheses. It is highly likely that the species of Polycopissa are a Tethyan relict and must have recently dispersed from an adjacent habitat to the current distribution area.