Decapods - Decapods

Japanese: 十脚類 - じっきゃくるい（英語表記）decapod

A general term for crustaceans in the order Decapoda of the class Malacostraca. Based on their basic body shape, they were often divided into three suborders: Longura (shrimps), Anomura (hermit crabs), and Brachyura (crabs). However, based on their ecological characteristics, they were once divided into two suborders: Swimming (most shrimps) and Walking (lobsters, crayfish, hermit crabs, and crabs). Today, they are generally divided into two suborders: Root-branchs (prawns and shrimps) and Ovoviviparous (most shrimps, hermit crabs, and crabs). The basic body structure is (1) a cephalothorax covered by a single carapace, (2) an abdominal region consisting of six segments and a telson segment, and (3) one to several pairs of chelipeds and several pairs of walking legs, but there are significant changes depending on the lineage and ecology. There are five pairs of head appendages (the first antenna for sensation, the second antenna and the mandible that forms the mouthparts, and the first and second maxillae), eight pairs of thoracic appendages (the first to third maxillae that form the mouthparts, and the first to fifth walking legs for movement), and six pairs of abdominal appendages consisting of the first to fifth abdominal appendages and the uropods. They generally have stalked compound eyes, and all breathing is done by gills. They are the most advanced class of crustaceans, with over 9,000 known species, from freshwater to the deep sea. (→Arthropods, Malacostraca)

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

Japanese:

軟甲綱十脚目 Decapodaとしてまとめられる甲殻類の総称。基本的な体型から，長尾類（エビ類），異尾類（ヤドカリ類），短尾類（カニ類）という 3亜目に分けられることが多かったが，生態的な特徴から遊泳類（多くのエビ類）と歩行類（イセエビ・ザリガニ類，ヤドカリ類，カニ類）という 2亜目に分類されたこともある。今日は，根鰓類（クルマエビ・サクラエビ類）と抱卵類（多くのエビ類，ヤドカリ類，カニ類）の 2亜目に分けるのが一般的である。基本的な体制は，(1) 頭胸部が 1枚の甲で覆われる，(2) 腹部が 6節と尾節からなる，(3) 1～数対の鋏脚と数対の歩脚をもつ，などであるが，系統および生態の相違による変化が著しい。頭部付属肢は 5対（感覚用の第1触角，第2触角と口器を形成する大顎および第1小顎，第2小顎），胸部付属肢は 8対（口器を形成する第1～3顎脚，運動用の第1～5歩脚），腹部付属肢 6対は第1～5腹肢と尾肢からなる。眼は一般に有柄の複眼で，呼吸はすべて鰓による。甲殻類中最も進んだ類で，淡水から深海まで約 9000種以上が知られている。（→節足動物，軟甲類）

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