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Deepwater stingray
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 . This species reaches in length and 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 probably aplacental viviparous, with the mother supplying her gestating young with histotroph ("uterine milk"). Captured rays merit caution due to their long, venomous stings. 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 (IUCN) has assessed it as Least Concern.
==Taxonomy and phylogeny==
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 (ORI), 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 across, and the paratype is an immature male across.〔 Other common names for this species include Davies' stingray and giant stingray.〔
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").〔 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'', and thus assigned it provisionally to the family Hexatrygonidae.〔 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.〔 Until the phylogeny is better-resolved, authors have tended to preserve the family Plesiobatidae.〔〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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