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Johngarthia lagostoma
''Johngarthia lagostoma'' is a species of terrestrial crab that lives on Ascension Island and three other islands in the South Atlantic. It grows to a carapace width of on Ascension Island, where it is the largest native land animal.〔 It exists in two distinct colour morphs, one yellow and one purple, with few intermediates. The yellow morph dominates on Ascension Island, while the purple morph is more frequent on Atol das Rocas. The species differs from other ''Johngarthia'' species by the form of the third maxilliped.
''Johngarthia lagostoma'' lives in burrows among vegetation, at altitudes of up to , emerging at night to feed on plant matter and occasionally on animals. From January to March there is an annual migration to the sea to release the planktonic larvae. The species was first described (as ''Gecarcinus lagostoma'') by Henri Milne-Edwards in 1837 from material sent to him by the naturalists Jean René Constant Quoy and Joseph Paul Gaimard, collected by the French ship ''Astrolabe''.
==Distribution and biogeography==
''Johngarthia lagostoma'' is found on Ascension Island, , and . On Ascension Island, ''J. lagostoma'' is restricted outside the breeding season to the slopes of Green Mountain, where there is sufficient moisture and vegetation, the rest of the island being too arid for the crab to survive.〔 All the land above is suitable habitat for the crabs, as is much of the land above .〔 They are occasionally found at lower altitudes, including the well-watered gardens of Georgetown, and the sooty tern breeding colony in the south-west of the island (known as the Wideawake Fairs).〔 On , ''J. lagostoma'' is abundant wherever plants grow, included the highest parts of the island.〔
The geographic distribution of ''J. lagostoma'' across a small number of islands in the southern Atlantic Ocean is very unusual, and difficult to explain by planktonic dispersal. Its nearest relatives are the other species of ''Johngarthia'', two of which (''J. malpilensis'' and ''J. planata'') inhabit islands in the Pacific Ocean off Central America, and one (''J. weileri'') is found on islands in the Gulf of Guinea.〔 Some authors have suggested the existence of former islands, now submerged, which could have acted as "stepping stones" for the colonisation of Ascension Island; the isolation of Ascension Island from any other land mass makes transportation of either larvae or adults difficult.〔
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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