Red crab (English name) Gecarcoidea natalis

Japanese: アカガニ（英語表記）Gecarcoidea natalis

A land crab of the order Decapoda of the class Malacostraca, family Geotrichum. It is a land crab with a carapace width of more than 10 cm, uniformly deep crimson red. It only lives on Christmas Island, an isolated island in the eastern Indian Ocean (there is also a record of it having once lived on the neighboring Cocos Keeling Islands). It lives in burrows dug underground in the rainforest, but in late autumn it moves toward the coast to spawn. There are said to be 120 million of them, and a red carpet-like swarm of crabs moves through human settlements for more than a week. Males form a leading group, digging holes near the sea and waiting for females to follow. After mating, the females wait several weeks for the eggs to mature, and on the night of a spring tide, they release the larvae at the water's edge and return to the forest. After a few weeks, the juvenile crabs, with a carapace width of a few millimeters, walk toward the forest. Another species of this genus is called the purple land crab G. lalandii because of its body color, and is widely distributed in the Ryukyu Islands and islands in the southwest Pacific Ocean. This genus of crabs can be easily distinguished from other land crabs (→ Land crabs) because their eye sockets are close together (narrow foreheads). Because the name of the red crab is so simple, it is sometimes called the Christmas red crab. (→ Crustacea, Decapods, Arthropods, Malacostraca)

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

軟甲綱十脚目オカガニ科。甲幅 10cm以上になる陸生のカニで，一様に濃い朱赤色。インド洋東部の孤島，クリスマス島にのみ生息する（隣接のココスキーリング諸島にもかつて生息していた記録がある）。熱帯雨林の土中に巣穴を掘ってすんでいるが，晩秋になると産卵のために海岸を目指して移動する。その数は 1億2000万匹といわれ，赤い絨毯のようなカニの群れが 1週間以上にわたり人里を通って移動する。雄が先頭集団を形成し，海に近い場所に穴を掘って，後続の雌を待つ。交尾後，雌は卵が成熟するのを数週間待ち，大潮の夜，水際で幼生を放って森に戻る。数週間後には甲幅数mmの稚ガニが森を目指して歩く。この属のもう一種はその体色からムラサキオカガニ G. lalandii と呼ばれ，琉球列島，南西太平洋の島々に広く分布している。この属のカニは，左右の眼窩が接近している（額が狭い）ことで，ほかのオカガニ類（→オカガニ）とは容易に区別することができる。アカガニの名があまりにも単純であるため，クリスマスアカガニと呼ぶこともある。（→甲殻類，十脚類，節足動物，軟甲類）

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