Janinecaira darkthread n. gen., n. sp. (Eudactylinidae, Siphonostomatoida, Copepoda) infects gills of the ornate eagle ray Aetomylaeus vespertilio (Bleeker, 1852) (Myliobatidae, Myliobatiformes) in the Beagle Gulf (Timor Sea, eastern Indian Ocean) off northern Australia. The adult female of Janinecaira darkthread n. sp. is most easily distinguished from other eudactylinids (Eudactylinidae) by its long genital complex that comprises about 86–90% of the total body length. A diagnostic key to genera of Eudactylinidae based on adult females is provided.