A general term for coelenterates (cnidarians) of the class Hydrozoa, which are divided into five orders. Some species remain only in the sedentary polyp form, only in the swimming jellyfish form, or alternate between polyp and jellyfish forms during their lifetime. The structure of a polyp (illustration) is simple, with no septum in the stomach cavity and tentacles surrounding the mouth plate. Polyps such as Hydra, Otohime no hanabu (illustration), and Kudahidira are single polyps, but most polyps attach to other objects by extending rhizoids and form branched hydrocaulus to form colonies. Source: Heibonsha World Encyclopedia, 2nd Edition Information |
ヒドロ虫綱Hydrozoaの腔腸動物(刺胞動物)の総称で,5目に分けられる。一生の間,定着性のポリプ型のみ,あるいは遊泳性のクラゲ型のみ,またはポリプ型からクラゲ型を経て世代の交替をするものがある。ポリプの体制(イラスト)は簡単で,胃腔内に隔膜がなく,口盤の周辺部を触手がとりまいている。ヒドラ,オトヒメノハナガサ(イラスト),クダウミヒドラなどは単体であるが,大部分のポリプは仮根をだして他物に付着し,枝分れしたヒドロ茎hydrocaulusをつくって群体を形成する。
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