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sharptooth houndshark
The sharptooth houndshark, or spotted gully shark (''Triakis megalopterus''), is a species of houndshark, belonging to the family Triakidae, found in shallow inshore waters from southern Angola to South Africa. Favoring sandy areas near rocky reefs and gullies, it is an active-swimming species that usually stays close to the bottom. This robust shark reaches in length and has characteristically large, rounded fins; the pectoral fins in particular are broad and sickle-shaped in adults. It also has a short, blunt snout and long furrows around its mouth. This species is gray or bronze in color above, with variable amounts of black spotting.
Mainly active at night, the sharptooth houndshark feeds mostly on crustaceans, bony fishes, and cephalopods. It has been observed gathering in groups in shallow water during summertime, possibly for reproductive purposes. This species is aplacental viviparous, meaning that the unborn young are sustained mainly by yolk. Females give birth to 6–12 pups between late May and August, on a two- or three-year cycle. The sharptooth houndshark is often hooked by recreational anglers, and some are also captured on commercial bottom longlines. Because of its small range, its low growth and reproductive rates, it is very vulnerable to overfishing. The International Union for Conservation of Nature (IUCN) has therefore listed this species as Near Threatened.
==Taxonomy and phylogeny==
Scottish zoologist Andrew Smith originally described the sharptooth houndshark as a species of ''Mustelus'' in 1839, as part of his work ''Illustrations of the Zoology of South Africa''. His account was based on two specimens caught off the Cape of Good Hope, South Africa. Smith named the shark ''megalopterus'', from the Greek ''mega'' ("large") and ''pteron'' ("wing"), referring to its large fins.〔〔 Another common name for this shark is "sweet William".〔
Later authors have reassigned the sharptooth houndshark to the genus ''Triakis'', more specifically to the subgenus ''Cazon'' alongside the sharpfin houndshark (''T. acutipinna'') and the spotted houndshark (''T. maculata'').〔 A 2006 phylogenetic study by J. Andrés López and colleagues, based on four protein-coding gene sequences, found that this species did not group with the leopard shark (''T. semifasciata''). Instead, it and the flapnose houndshark (''Scylliogaleus quecketti'') formed a clade within the ''Mustelus'' lineage. This result suggests that the two subgenera of ''Triakis''—''Cazon'' and ''Triakis''—may not be closely related, which would warrant a redefinition of the genus.〔
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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