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Horseshoe crabs are marine arthropods of the family Limulidae and order Xiphosura or Xiphosurida, that live primarily in and around shallow ocean waters on soft sandy or muddy bottoms. They occasionally come onto shore to mate. They are commonly used as bait and in fertilizer. In recent years, a decline in the population has occurred as a consequence of coastal habitat destruction in Japan and overharvesting along the east coast of North America. Tetrodotoxin may be present in the roe of species inhabiting the waters of Thailand. Because of their origin 450 million years ago (Mya), horseshoe crabs are considered living fossils. ==Classification== Horseshoe crabs resemble crustaceans, but belong to a separate subphylum, Chelicerata, and are closely related to arachnids. The earliest horseshoe crab fossils are found in strata from the late Ordovician period, roughly 450 million years ago... The Limulidae are the only recent family of the order Xiphosura, and contain all four living species of horseshoe crabs: * ''Carcinoscorpius rotundicauda'', the mangrove horseshoe crab, found in Southeast Asia * ''Limulus polyphemus'', the Atlantic horseshoe crab, found along the American Atlantic coast and in the Gulf of Mexico * ''Tachypleus gigas'', found in Southeast and East Asia * ''Tachypleus tridentatus'', found in Southeast and East Asia 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「horseshoe crab」の詳細全文を読む スポンサード リンク
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