The deepwater stingray or giant stingaree (Plesiobatis daviesi) is a species of stingray and the sole member of the family Plesiobatidae. It is widely distributed in the Indo-Pacific, typically over fine sediments on the upper continental slope at depths of 275–680 m (900–2,230 ft). This species reaches 2.7 m (8.9 ft) in length and 1.5 m (4.9 ft) in width. It has an oval pectoral fin disc with a long, flexible, broad-angled snout. Most of the entire latter half of its tail supports a distinctively long, slender, leaf-shaped caudal fin. Its coloration is dark above and white below, and its skin is almost completely covered by tiny dermal denticles.
Preying on crustaceans, cephalopods, and bony fishes, the deepwater stingray may hunt both on the sea floor and well above it in open water. It is likely aplacental viviparous, with the mother supplying her gestating young with histotroph ("uterine milk"). Captured rays merit caution due to their long, venomous stingers. This species is taken by deepwater commercial fisheries, but in numbers too small to significantly threaten its population. Therefore, the International Union for Conservation of Nature has assessed it as Least Concern.
The first scientific description of the deepwater stingray was authored by John H. Wallace, as part of a 1967 Investigational Report from the Oceanographic Research Institute, Durban. He named the new species daviesi in honor of David H. Davies, the late director of the ORI, and placed it in the genus Urotrygon based on its long, low caudal fin and lack of a dorsal fin. The type specimens were collected during September 1996 near the Limpopo River mouth in Mozambique: the holotype is a mature male 92 cm (36 in) across, and the paratype is an immature male 33 cm (13 in) across.[3] Other common names for this species include Davies' stingray and giant stingray.[4]
In a 1990 morphological phylogenetic study, Kiyonori Nishida concluded that the deepwater stingray and the sixgill stingray (Hexatrygon bickelli) were the most basal stingrays (suborder Myliobatoidei). Therefore, he moved this species to its own genus, Plesiobatis, and family, Plesiobatidae; the name is derived from the Greek plesio ("primitive") and batis ("ray").[5] Subsequent morphological studies have corroborated the basal position of Plesiobatis, but disagreed on its relationships to nearby taxa. John McEachran, Katherine Dunn, and Tsutomu Miyake in 1996 could not fully resolve the position of Plesiobatis, thus they assigned it provisionally to the family Hexatrygonidae.[6] McEachran and Neil Aschliman in 2004 found Plesiobatis to be the sister taxon of Urolophus, and recommended that it be placed in the family Urolophidae.[7] Until the phylogeny is better-resolved, authors have tended to preserve the family Plesiobatidae.[2][8]
Records of the deepwater stingray come from a number of locations scattered widely in the Indo-Pacific: KwaZulu-Natal in South Africa and Mozambique, the Gulf of Mannar, the northern Andaman Islands, the South China Sea, the Ryukyu Islands and the Kyushu–Palau Ridge, along the southern coastline of Australia, northwestern Australia from the Rowley Shoals to Shark Bay, northeastern Australia from Townsville to Wooli, New Caledonia, and Hawaii.[1][9][10][11] This bottom-dwelling species generally inhabits the upper continental slope at depths of 275–680 m (900–2,230 ft), over muddy or silty substrates.[11] An anomalous record from only 44 m (144 ft) deep off Mozambique was made. It seems to be locally common in tropical Australian waters, but may be rarer elsewhere.[1]