What is "chaetognatha"

Chaetognatha \Chae*tog"na*tha\, ||Chaetognatha \Ch[ae]*tog"na*tha\, n. pl. [NL., from Gr. ? hair + ? jaw.] (Zo["o]l) 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.

Syn: phylum Chaetognatha.

Chaetognatha, meaning bristle-jaws, and commonly known as arrow worms, is a phylum of predatory marine worms which 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 polar regions. Most chaetognaths are transparent and are torpedo shaped, but some deep-sea species are orange. They range in size from .

There are more than 120 modern species assigned to over 20 genera. Despite the limited diversity of species, the number of individuals is large.