Invaginated Kiss - Kannyuufun

…The proboscis of kinorhyncha, nematodes, helminths, and stag beetles is the front end of the body with a mouth at the tip, which can be retracted into the body at the rear, and generally has small and large spines on its surface. The proboscis of stag beetles is also an extension of the front end of the body that continues to the mouth, but since it can be retracted inside out so that the mouth falls into the body, it is called an introvert proboscis. The proboscis of stag beetles is an extension that protrudes and elongates around the mouth at the front end of the body in a groove-like shape, and cannot be retracted into the body. …

*Some of the terminology explanations that mention "invagination" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…動吻類，線形虫類，コウトウチュウ類，エラヒキムシ類などの吻は，先端に口をもった体前端部で，後方の体内に引っ込めることができ，表面には一般に大小のとげがある。ホシムシ類の吻も口に続く体前端部が伸長したものであるが，これは口が体内へ落ち込むように裏返しになって引っ込められるので，陥入吻introvertと呼ばれる。ユムシ類の吻は，体の前端の口の周囲が溝状に突出，伸長したもので，体内に引っ込めることはできない。…

※「陥入吻」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