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Sawfishes, also known as carpenter sharks, are an order (Pristiformes) of rays characterized by a long, narrow, flattened rostrum, or nose extension, lined with sharp transverse teeth, arranged so as to resemble a saw. Several species of sawfishes can grow to about . The family as a whole is largely unknown and little studied. The Pristidae are the only living family within the order Pristiformes, whose name comes from the . Sawfishes should not be confused with sawsharks (order Pristiophoriformes), which have a similar appearance. All species of sawfishes are listed as Endangered or Critically Endangered by the IUCN, and face the threat of extinction as a result of habitat loss and overfishing. Global populations of every species of sawfishes are estimated to have fallen to less than 10% of their historic levels, and they have been lost from at least 80% of their historic range.〔 〕 The smalltooth sawfish (''Pristis pectinata''), for example, was once widely distributed, but available data indicate the range of this species has been reduced by about 90%, and population numbers have declined dramatically, perhaps by 95% or more.〔 International commerce of sawfishes has been banned globally since 2007, with the only exception being for the provision of live ''Pristis microdon'' to appropriate public aquaria for primarily conservation purposes.〔(【引用サイトリンク】title=CITES Appendices I, II and III )〕 == Description == The sawfish's most distinctive feature is the saw-like rostrum, covered with electrosensitive pores that allow the sawfish to detect slight movements of prey hiding in the muddy sea floor. The rostrum also serves as a digging tool to unearth buried crustaceans. Should suitable prey try to swim past, the normally lethargic sawfish springs from the bottom and slashes at it with its saw. This generally stuns or impales the prey sufficiently for the sawfish to devour it. Sawfish also defend themselves with their rostrum against intruding divers and predators such as sharks. The "teeth" protruding from the rostrum are not real teeth, but modified tooth-like structures called denticles. The body and head of a sawfish are flat, and they spend most of their time lying on the sea floor. Like rays, a sawfish's mouth and nostrils are on its flat underside. The mouth is lined with small, dome-shaped teeth for eating small fish and crustaceans, which the fish sometimes swallows whole. Sawfish breathe with two spiracles just behind the eyes that draw water to the gills. The skin is covered with tiny dermal denticles that give the fish a rough texture. Sawfish are usually light grey or brown; the smalltooth sawfish, ''Pristis pectinata'', appears olive green. Like other elasmobranchs, sawfish lack a swim bladder and use a large, oil-filled liver to control buoyancy. Their skeleton is made of cartilage. The eyes of the sawfish are underdeveloped due to their muddy habitats. The rostrum is the main sensory device. Their small intestines contain an internal partition shaped like a corkscrew, called a spiral valve, which increases the surface area available for food absorption. The smallest sawfish is the dwarf sawfish (''P. clavata''), which grows to , much smaller than the others. The largest species seem to be the large-tooth sawfish (''P. microdon''), the Leichhardt's sawfish (''P. perotteti''), and the common sawfish (''P. pristis''), which can all reach about in length.〔〔〔 One southern sawfish was recorded as weighing .〔(【引用サイトリンク】title=Big Fish Stories )〕 Such massive specimens that survive long enough to approach their maximum size and age are believed to have lifespans of about 51 years.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「sawfish」の詳細全文を読む スポンサード リンク
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