a phylum consisting of the arrowworms, a group of small active transparent free-swimming marine worms, of which the genus Sagitta is the type. They have groups of curved spines on each side of the head.

Chaetognatha is a phylum of predatory marine worms that are a major component of plankton worldwide. They show some preference for warmer waters. Chaetognaths are transparent and are torpedo shaped sometimes with arrowhead like opaque structures in their heads.