A new Category 1 species of Acanthobothrium van Beneden, 1850 is described from the cowtail stingray Pastinachus atrus (Macleay) collected from the Gulf of Carpentaria near Weipa, Queensland, Australia. This species is unique among Acanthobothrium Category 1 species in that it retains gravid proglottids on its strobila. It differs further from the 34 other Category 1 species in total length, proglottid number and testis number. The host identities of other Acanthobothrium species reported from Pastinachus are revised based on recent taxonomic work on rays of this genus. Given the revised host taxonomy, according to which P. atrus is the only member of its genus occurring off Australia, this should be considered to be the fifth species of Acanthobothrium reported from this Australian endemic species.