A new genus of groundwater Ameiridae (Copepoda, Harpacticoida) from boreholes in Western Australia and the artificial status of Stygonitocrella Petkovski, 1976

Examination of the copepod fauna inhabiting 50m deep production bores on Barrow Island (northwestern Australia), resulted in the discovery of an unusual ameirid which cannot be placed in any extant genus. Both sexes are characterized by a unisetose antennary exopod and extreme reduction in the swimming legs (particularly the endopods) and P5. Males lack a defined P6 closing off the single genital aperture and have an extraordinarily large spermatophore. Females similarly display a highly reduced genital field. The new species shows superficial similarities to both Psammonitocrella Rouch and Stygonitocrella Reid, Hunt & Stanley, however the combined presence of a sexually dimorphic inner basal spine on P1, a completely fused genital double-somite, reduced antennary exopod and vestigial P5 excludes it from either genus. Some problems in the current classification of freshwater Ameiridae are highlighted, with particular reference to the genus Stygonitocrella . A new genus Neonitocrella is proposed for Stygonitocrella insularis (Miura, 1962).