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The bichirs and reedfish (also called ropefish) comprise the Polypteridae, a family of archaic-looking ray-finned fishes and the sole family in the order Polypteriformes.〔Helfman GS, Collette BB, Facey DE, Bowen BW. 2009. The Diversity of Fishes. West Sussex, UK: Blackwell Publishing. 720 p.〕 All species occur in freshwater habitats in tropical Africa and the Nile River system, mainly swampy, shallow floodplains and estuaries. Bichirs are considered the sister group to all other extant ray-finned fishes. ==Anatomy== Bichirs are elongated fish with a unique series of dorsal finlets which vary in number from seven to 18, instead of a single dorsal fin. Each of the dorsal finlets has bifid (double-edged) tips, and are the only fins with spines; the rest of the fins are composed of soft rays. The body is covered in thick, bonelike, and trapezoidal (ganoid) scales. Their jaw structure more closely resembles that of the tetrapods than that of the teleost fishes. Bichirs have a number of other primitive characteristics, including fleshy pectoral fins superficially similar to those of lobe-finned fishes. They also have a pair of slit-like spiracles used to exhale air, two gular plates, and paired ventral lungs (the left lung shorter than the right).〔Berra, Tim M. (2001). Freshwater Fish Distribution. San Diego: Academic Press. ISBN 0-12-093156-7〕 Four pairs of gill arches are present.〔(AccessScience | Encyclopedia Article | Polypteriformes )〕 Bichirs have a maximum body length of .〔 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「Bichir」の詳細全文を読む スポンサード リンク
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