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The use of integrative taxonomy has confirmed the existence of a new distinct crab species, cryptic, within the group of the former genus Liocarcinus, now Polybius, closely related to P. holsatus, P. vernalis and P. marmoreus. Previous reports have considered it to be the Atlantic form of P. vernalis, or as a species “affinis” or “comparable to” P. holsatus. Diagnostic morphological characters are presented for identification and the morphological variability in these species, mainly within P. vernalis (the most related) is analysed. Furthermore, based on molecular and other previous data, a new combination (genus change) is proposed. This new species, Polybius dioscurus sp. nov., lives on infralittoral sandy bottoms, coexisting with the other species mentioned, in the temperate and subtropical zone of the North Atlantic Ocean, including the Alboran Sea (westernmost Mediterranean).
Background: The faunal and floral relationship of northward-drifting India with its neighboring continents is of general biogeographic interest as an important driver of regional biodiversity. However, direct biogeographic connectivity of India and Southeast Asia during the Cenozoic remains largely unexplored. We investigate timing, direction and mechanisms of faunal exchange between India and Southeast Asia, based on a molecular phylogeny, molecular clock-derived time estimates and biogeographic reconstructions of the Asian freshwater crab family Gecarcinucidae. Results: Although the Gecarcinucidae are not an element of an ancient Gondwana fauna, their subfamily Gecarcinucinae, and probably also the Liotelphusinae, evolved on the Indian Subcontinent and subsequently dispersed to Southeast Asia. Estimated by a model testing approach, this dispersal event took place during the Middle Eocene, and thus before the final collision of India and the Tibet-part of Eurasia. Conclusions: We postulate that the India and Southeast Asia were close enough for exchange of freshwater organisms during the Middle Eocene, before the final Indian--Eurasian collision. Our data support geological models that assume the Indian plate having tracked along Southeast Asia during its move northwards.