Hectocotylized arm

Japanese: 交接腕 - こうせつわん（英語表記）hectocotylized arm

This refers to a certain arm of the male cephalopod mollusks that is modified for the purpose of passing the spermatophore (also called spermatophore) to the female during mating. It is also called the reproductive arm or metapod arm. In octopods, it is often the third right arm, and in decapoda, it is often the fourth right or left (or both) arm. In octopuses such as the giant octopus and the giant octopus, this arm breaks off after mating and remains in the female's mantle cavity, moving like an insect. GL Cuvier thought it was a parasite and named it hectocotylus (a hundred warts), and the hectocotyl is still called that today.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

軟体動物頭足類の雄の一定の腕が，交接に際し雌に精莢（せいきよう）spermatophore(精包ともいう)を渡す目的のため変形しているものをいう。生殖腕または化茎腕ともいわれる。八腕形類では右第3腕の場合が多く，十腕形類では右または左(または両側)の第4腕の場合が多い。アミダコやカイダコなどでは交接後この腕が切れ，雌の外套腔内に残っていて虫のように動くので，これをG.L.キュビエは寄生虫と思いヘクトコチルス(百疣虫（ひやくいぼちゆう）)と名づけたところから現在も交接腕はそう呼ばれている。

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

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