A primitive representative of the Parabathynellidae (Bathynellacea, Syncarida) from the Yilgarn Craton of Western Australia

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Abstract
Billibathynella humphreysi gen. et sp. nov. is described from calcrete aquifers located in the Yilgarn Craton of north‐western Australia. This is the first parabathynellid known from the Australian Precambrian shields, which have never been inundated by the sea. A comparison of the primitive species so far known from Australia and other continents points to the new species as being the most primitive among the parabathynellids. It further suggests that the new genus has an affinity to Notobathynella Schminke, but differs in having a six‐segmented antenna and a large epipod of the male thoracopod VIII. An attempt to relate the primitiveness of the new species to the historiogeological characteristics of the region has led to the conclusion that the recent parabathynellids could have emerged from freshwater epigean ancestors. It is further assumed that the transition of their ancestors to groundwaters happened in Notogaea.