noun
acorn worm
Refers to any hemichordate of the class Enteropneusta. A technical term in zoology; in everyday contexts, it is rarely encountered.
干潟でギボシムシの巣穴を見つけた。
I found acorn worm burrows on the tidal flat.
ギボシムシは半索動物に分類される。
Acorn worms are classified as hemichordates.
The name ギボシムシ comes from the shape of the proboscis, which resembles a 擬宝珠 (giboshi), a traditional ornamental cap on bridge posts and railings. The derivation is straightforward, but the word is a modern coinage for this animal group.