Dictionary:

chaetognath

  (kē'tŏg-năth')

Any of various marine worms of the phylum Chaetognatha, which includes the arrow worms.

Of, relating to, or belonging to the phylum Chaetognatha.

[From New Latin Chaetognatha, phylum name : chaeta, chaeta; see chaeta + Greek gnathos, jaw.]

The noun has one meaning:

Meaning #1: 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
  Synonym: arrowworm