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The Louisiana pearlshell, ''Margaritifera hembeli'', is a rare species of bivalve in the Margaritiferidae family. This freshwater mussel is native to Louisiana in the United States. It also once occurred in Arkansas, but it has been extirpated from all the waterways there.〔(''Margaritifera hembeli''. ) The Nature Conservancy.〕 It is a federally listed threatened species of the United States. This mussel reaches about 10 centimeters long by 5 wide and 3 high. It is dark brown or black in color with a white nacre.〔USFWS. (Final endangered status for Louisiana Pearlshell (''Margaritifera hembeli''). ) ''Federal Register'' February 5, 1988.〕 When it was first placed on the Endangered Species List in 1988 the mussel was thought to remain only in the Bayou Boeuf river system in Rapides Parish, Louisiana. It was found in eleven streams with 90% of the total population found in four of the streams.〔 The mussel was downlisted to threatened status in 1993 when more populations were discovered. It was found to inhabit eight streams in the Red River drainage in Grant Parish, Louisiana.〔USFWS. (Determination to reclassify the Louisiana Pearlshell (''Margaritifera hembeli'') from endangered to threatened. ) ''Federal Register'' September 24, 1993.〕 This mussel lives in small, shallow creeks with sandy or gravel bottoms. They are found more often in riffles and areas with faster currents than in stagnant pools. The water is clear and the substrate is stable.〔 Like other freshwater mussels, this species releases its larvae, termed glochidia, into the water where they enter the bodies of fish as parasites to develop into juvenile mussels. Host fish species for this mussel include striped shiner (''Luxilus chrysocephalus''), redfin shiner (''Lythrurus umbratilis''), golden shiner (''Notemigonus crysoleucas''),〔 and brown madtom (''Noturus phaeus'').〔Johnson, P. D. and K. M. Brown. (1998). (Intraspecific life history variation in the threatened Louisiana pearlshell mussel, ''Margaritifera hembeli''. ) ''Freshwater Biology'' 40(2) 317-29.〕 This species is threatened by the loss and degradation of its habitat. These habitat changes are caused by impoundments of the waterways, including the effects of beaver dams. Some areas, including streams in the Kisatchie National Forest, undergo increased sedimentation from nearby silviculture, road maintenance, and livestock grazing. Gravel mining may also cause increased sediment.〔 Genetic analysis reveals the species has low genetic variability, which makes it more vulnerable to changes in its environment. ==References== 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「Louisiana pearlshell」の詳細全文を読む スポンサード リンク
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