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Borneo shark
The Borneo shark (''Carcharhinus borneensis'') is a species of requiem shark, and part of the family Carcharhinidae. Extremely rare, it is known only from inshore waters around Mukah in northwestern Borneo, though it may once have been more widely distributed. A small, gray shark reaching in length, this species is the only member of its genus with a row of enlarged pores above the corners of its mouth. It has a slender body with a long, pointed snout and a low second dorsal fin placed posterior to the anal fin origin.
Almost nothing is known about the natural history of the Borneo shark. It is viviparous like other requiem sharks; the females bear litters of six pups, which are provisioned through gestation by a placental connection. The International Union for Conservation of Nature last assessed this species as Endangered, at which time it had not been seen since 1937. While an extant population has since been found, the Borneo shark continues to merit conservation concern given its highly limited range within heavily fished waters.
==Taxonomy and phylogeny==
Dutch ichthyologist Pieter Bleeker originally described the Borneo shark as ''Carcharias (Prionodon) borneensis'' in an 1858 issue of the scientific journal ''Acta Societatis Regiae Scientiarum Indo-Neêrlandicae''. He based his account on a newborn male long, caught off Singkawang in western Kalimantan, Borneo.〔 Later authors have recognized this species as belonging to the genus ''Carcharhinus''.〔 Before 2004, only five specimens of the Borneo shark were known, all of them immature and collected before 1937.〔 In April and May 2004, researchers from Universiti Malaysia Sabah discovered a number of additional specimens while surveying the fishery resources of Sabah and Sarawak.〔
The evolutionary relationships of the Borneo shark are uncertain. Jack Garrick, in his 1982 morphological study, did not place it close to any other member of the genus.〔 Leonard Compagno in 1988 tentatively grouped it with the smalltail shark (''C. porosus''), blackspot shark (''C. sealei''), spottail shark (''C. sorrah''), creek whaler (''C. fitzroyensis''), whitecheek shark (''C. dussumieri''), hardnose shark (''C. macloti''), and Pondicherry shark (''C. hemiodon'').〔 The Borneo shark resembles the sharpnose sharks (''Rhizoprionodon'') in certain traits, for example the enlarged pores by its mouth. Nevertheless, other aspects of its morphology firmly place it within ''Carcharhinus''.〔
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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