noun
archiannelid of genus Saccocirrus; Saccocirrus major
A small marine worm; used primarily in zoological contexts. The katakana spelling is standard.
ムカシゴカイは潮間帯の砂の中に生息する原始的な環形動物である。
Saccocirrus major is a primitive annelid that lives in the sand of intertidal zones.
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.