noun
arrow worm
A marine invertebrate of the phylum Chaetognatha; a technical zoological term.
See also: 毛顎動物
プランクトンサンプルからヤムシが見つかった。
Arrow worms were found in the plankton sample.
毛顎動物 is the formal Japanese name for the phylum Chaetognatha, while ヤムシ is the common name for arrow worms.
The name ヤムシ (矢虫) literally means 'arrow insect/worm', referring to the arrow-like shape of these animals. The exact derivation is uncertain.