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The marsh shrew (''Sorex bendirii''), also known as the Pacific water shrew, Bendire's water shrew and Bendire's shrew, is the largest North American member of the genus ''Sorex'' (long-tailed shrews). Primarily covered in dark-brown fur, it is found near aquatic habitats along the Pacific coast from southern British Columbia to northern California. With air trapped in its fur for buoyancy, marsh shrews can run for three to five seconds on top of the water. It measures about in length, including a -long tail, and weighs an average of . The marsh shrew's diet consists mainly of invertebrates, which it hunts on land and in the water. They are rare; their populations are thought to be in decline, and they are considered endangered in parts of their range. ==Description== The marsh shrew is the largest member of the genus ''Sorex'' in North America, and mammalogist David Nagorsen described it as "an attractive mammal". Its fur is primarily dark brown, and it has a long tail. Although the marsh shrew's fur is usually uniformly dark on its back and abdomen, the abdominal fur of populations (''S. b. albiventer'') on the Olympic Peninsula may be white. The marsh shrew is about in length, including a -long tail, and weighs about . Its hind feet, slightly fringed with coarse hairs on the toes, measure about . Although in some areas the marsh shrew is sympatric with other members of the genus ''Sorex'', no other large, velvety, gray-black shrew shares this geographic range. Its size distinguishes it from all but the American water shrew (''Sorex palustris''). Although the marsh shrew and the American water shrew (the two largest shrews in North America) share some features, the American water shrew has more dark-grey-to-black fur on its back, a silver-grey belly and a bi-colored tail and the marsh shrew's fringed hairs are more distinct. The American water shrew has a smaller skull, without the marsh shrew's characteristic curvature, and its upper incisors have less-distinct medial tines. The marsh shrew typically has a longer snout than that of the American water shrew, which is more streamlined when viewed from the side. The marsh shrew's skull is relatively large, and its condylobasal skull length is usually greater than . There is a distinctive, downward-sloping curve along the snout (rostrum). Its dental formula is incisors: 1/1; unicuspids: 5/1; premolars: 1/1; molars: 3/3. Of the five upper unicuspids the third is distinctly smaller than the fourth, and they have a pigmented ridge extending to the cingulum. There is a large medial tine on the large upper incisor, in the anterior pigmented region. The reddish pigmentation of the enamel, the result of iron deposits, is thought to be an adaptation strengthening the enamel. There are no known fossil remains. The marsh shrew's karyotype somatic number is 2n = 54, and its fundamental number = 70. 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「marsh shrew」の詳細全文を読む スポンサード リンク
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