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The coconut crab, ''Birgus latro'', is a species of terrestrial hermit crab, also known as the robber crab or palm thief. It is the largest land-living arthropod in the world, and is probably at the upper size limit for terrestrial animals with exoskeletons in recent Earth atmosphere, with a weight of up to . It can grow to up to in length from leg to leg. It is found on islands across the Indian Ocean and parts of the Pacific Ocean as far east as the Gambier Islands mirroring the distribution of the coconut palm; it has been extirpated from most areas with a significant human population, including mainland Australia and Madagascar. The coconut crab is the only species of the genus ''Birgus'', and is related to the terrestrial hermit crabs of the genus ''Coenobita''. It shows a number of adaptations to life on land. Like hermit crabs, juvenile coconut crabs use empty gastropod shells for protection, but the adults develop a tough exoskeleton on their abdomen and stop carrying a shell. Coconut crabs have organs known as "branchiostegal lungs", which are used instead of the vestigial gills for breathing. They cannot swim, and will drown if immersed in water for long. They have developed an acute sense of smell, which has developed convergently with that of insects, and which they use to find potential food sources. Mating occurs on dry land, but the females migrate to the sea to release their fertilised eggs as they hatch. The larvae are planktonic for 3–4 weeks, before settling to the sea floor and entering a gastropod shell. Sexual maturity is reached after about 5 years, and the total lifespan may be over 60 years. Adult coconut crabs feed on fruits, nuts, seeds, and the pith of fallen trees, but will eat carrion and other organic matter opportunistically. The species is popularly associated with the coconut, and has been widely reported to climb trees to pick coconuts, which it then opens to eat the insides. While coconut crabs can climb trees, and can eventually open a coconut collectively, coconuts are not a significant part of their diet. Coconut crabs are hunted wherever they come into contact with people and are subject to legal protection in some areas. In the absence of precise information the IUCN lists the species as ''Data Deficient''. ==Description== ''Birgus latro'' is the largest terrestrial arthropod, and indeed terrestrial invertebrate, in the world;〔〔 reports about the size of ''Birgus latro'' vary, but most sources give a body length of up to ,〔 a weight of up to , and a leg span of more than ,〔 with males generally being larger than females.〔Drew ''et al.'' (2010), p. 49〕 The carapace may reach a length of , and a width of up to .〔Drew ''et al.'' (2010), p. 46〕 The body of the coconut crab is, like that of all decapods, divided into a front section (cephalothorax), which has 10 legs, and an abdomen. The front-most pair of legs has large chelae (claws), with the left being larger than the right.〔 The next two pairs, as with other hermit crabs, are large, powerful walking legs with pointed tips, which allow coconut crabs to climb vertical or overhanging surfaces.〔 The fourth pair of legs is smaller with tweezer-like chelae at the end, allowing young coconut crabs to grip the inside of a shell or coconut husk to carry for protection; adults use this pair for walking and climbing. The last pair of legs is very small and is used by females to tend their eggs, and by the males in mating.〔 This last pair of legs is usually held inside the carapace, in the cavity containing the breathing organs. There is some difference in colour between the animals found on different islands, ranging from orange-red to purplish blue;〔 in most regions, blue is the predominant colour, but in some places, including the Seychelles, most individuals are red.〔 Although ''Birgus latro'' is a derived type of hermit crab, only the juveniles use salvaged snail shells to protect their soft abdomens, and adolescents sometimes use broken coconut shells to protect their abdomens. Unlike other hermit crabs, the adult coconut crabs do not carry shells but instead harden their abdominal terga by depositing chitin and chalk. Not being constrained by the physical confines of living in a shell allows this species to grow much larger than other hermit crabs in the family Coenobitidae.〔 Like most true crabs, ''B. latro'' bends its tail underneath its body for protection.〔 The hardened abdomen protects the coconut crab and reduces water loss on land, but has to be moulted periodically. Adults moult annually, and dig a burrow up to long in which to hide while vulnerable.〔 It remains in the burrow for 3 to 16 weeks, depending on the size of the animal.〔 After moulting, it takes 1 to 3 weeks for the exoskeleton to harden, depending on the animal's size, during which time the animal's body is soft and vulnerable, and it stays hidden for protection.〔 In: Brown & Fielder (1991)〕 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「coconut crab」の詳細全文を読む スポンサード リンク
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