1) Phylum 2) Phylum chaetognatha 
Chaetognatha, meaning bristle-jaws, and commonly known as arrow worms, are a phylum of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic, and can attach to algae and rocks. They are found in all marine waters, from surface tropical waters and shallow tide pools to the deep sea and p...
• (n. pl.) An order of free-swimming marine worms, of which the genus Sagitta is the type. They have groups of curved spines on each side of the head.
[n] - arrowworms: a group of small active transparent marine worms
phylum Chaetognatha noun arrowworms: a group of small active transparent marine worms