1) Any worm of the chaetognatha 2) Chaetognath 3) Worm 1) Chaetognath 2) Glassworm 
• (n.) A peculiar transparent worm of the genus Sagitta, living at the surface of the sea. See Sagitta.
any member of the invertebrate phylum Chaetognatha, a group of small wormlike marine animals with transparent to translucent or opaque arrow-shaped ... [2 related articles]
Ar'row·worm` noun (Zoology) A peculiar transparent worm of the genus Sagitta , living at the surface of the sea. See Sagitta . 
[n] - any worm of the Chaetognatha
chaetognath noun any worm of the Chaetognatha; transparent marine worm with horizontal lateral and caudal fins and a row of movable curved spines at each side of the mouth
any small, translucent marine worm of the phylum (or class) Chaetognatha, having lateral and caudal fins.