Giant Octopus - Giant Octopus

...Many species are rarely seen by the general public, but the common octopus (illustration) is one of them, with a strange shape that looks like a body squashed from front to back. Its umbrella membrane is wide, and the free parts of its arms are short, making it almost disk-shaped. Its internal sac is also low, and it seems to swim quietly by waving its umbrella membrane and fins in the middle layers near the bottom of the ocean at depths of about 100 to 1500 meters. Other octopuses with a similar body shape that are known to live in the waters off Japan include the Senbei octopus and the Oomen octopus. The octopus that is generally familiar to the public belongs to the latter category, lacking fleshy fins and no tentacles on its arms. ...

*Some of the terminology that refers to "giant octopus" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…一般の目にふれることはまれな種が多いが，なかでもメンダコ（イラスト）は，体が前後に押しつぶされたような奇妙な形のタコで，傘膜が広く，腕の遊離部分が短いためまるで円板状で，内臓囊も低く，水深100～1500mくらいの海底に近い中層を傘膜とひれをあおって静かに遊泳しているらしい。同様の体型をもつもので，日本近海にいるものではほかにセンベイダコ，オオメンダコなどが知られる。　一般になじみのあるタコは後者に属するタコで，肉ひれを欠き，腕に触毛もない。…

※「オオメンダコ」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報