archiannelid of genus Saccocirrus; Saccocirrus major
A small marine worm; used primarily in zoological contexts. The katakana spelling is standard.
Saccocirrus major is a primitive annelid that lives in the sand of intertidal zones.
Katakana spelling is standard for this biological term.
Kanji spelling is rare; the word is usually written in kana.
The name ムカシゴカイ (昔沙蚕) literally means 'ancient ragworm', reflecting its primitive annelid characteristics. The exact derivation is uncertain.