Urogymnus acanthobothrium sp. nov., a new euryhaline whipray (Myliobatiformes: Dasyatidae) from Australia and Papua New Guinea

The Mumburarr Whipray, <em>Urogymnus acanthobothrium</em> sp. nov. is described from a single specimen taken from the Cambridge Gulf, Western Australia, and from images of 10 other specimens from northern Australia and Papua New Guinea (all observed but not collected). It is a very large ray that attains at least 161 cm disc width, making it amongst the largest of the whiprays. The ventral tail below the caudal sting has a low, short-based fold. A ventral tail fold (or a dorsal fold) has not been recorded for any other himanturin stingray in the Indo-West Pacific. Molecular data suggest it is most closely related to a similar but more widely distributed cognate, <em>U. granulatus</em>. Both of these species share a suboval disc shape, similar squamation patterns, and the tail posterior to the sting is entirely white (at least in small individuals). <em>U. acanthobothrium</em> sp. nov. differs from <em>U. granulatus</em> in having a longer and more angular snout, longer tail, more posteriorly inserted caudal sting, lacks white flecks on the dorsal surface, and the ventral disc is uniformly white (rather than white with a broad black margin). It co-occurs with two other morphologically distinct <em>Urogymnus</em> in the region (<em>U. asperrimus</em> and <em>U. dalyensis</em>). Like <em>U. dalyensis</em> it occurs in both brackish and marine waters. A key is proved to the members of the genus <em>Urogymnus</em>.