Crab - Crab

Japanese: カニ(蟹) - カニ

A general term for the brachyura of the class Crustacea. Like shrimp and hermit crabs, it consists of a cephalothorax and abdomen, but the abdomen is reduced in size and the muscles have degenerated. It has five pairs of thoracic legs, the first of which becomes a pair of claws and is useful for feeding, defense, and attack. The abdomen is usually narrow in males and wide in females. The eggs develop attached to the female's abdomen, hatching at the zoea stage and passing through the megalopa stage to become an adult. It is distributed widely from the polar zone to the tropics, but there are many species that live on continental shelves, rocky reefs, and coral reefs. The spider crab is the largest in the world, with a claw spread of 2 to 3 meters, and is a species endemic to Japan. The smallest is the Japanese giant spider crab, with a carapace width of 2.8 mm. It has a wide range of adaptations, including purely freshwater crayfish, Sesbania juncea, which is transitioning to a terrestrial lifestyle, and parasitic pincer crabs. The Japanese mitten crab is famous as an intermediate host of the pulmonary fluke. Many species are important as fishery resources, such as the blue crab, snow crab, and hairy crab. Coconut crab and red king crab resemble crabs, but have three pairs of walking legs, and, along with hermit crabs, belong to the Anomura.
→ Related topics Crustaceans

Source : Heibonsha Encyclopedia About MyPedia Information

Japanese:

甲殻綱短尾類の総称。エビ，ヤドカリ類と同様，頭胸部と腹部からなるが，腹部は縮小し，筋肉も退化している。胸脚は５対，第１胸脚ははさみになって摂食，防御，攻撃などに役だつ。腹部は普通雄では幅が狭く，雌では広い。卵は雌の腹部に付着したまま発育し，ゾエア期で孵化(ふか)，メガロパ期を経て成体になる。寒帯〜熱帯に広く分布するが，陸棚，岩礁，サンゴ礁にすむ種は特に多い。タカアシガニは世界最大で，はさみを広げると２〜3m，日本特産種である。最小は日本産のマメガニダマシで甲幅2.8mm。純淡水産のサワガニ，陸上生活に移りつつあるベンケイガニ，寄生性のカクレガニなど適応は広い。モクズガニは肺臓ジストマの中間宿主として有名。ガザミ，ズワイガニ，ケガニなど水産資源として重要な種類も多い。ヤシガニ，タラバガニなどはカニに似るが歩脚は３対で，ヤドカリとともに異尾類に属する。
→関連項目甲殻類

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