Arrow worms. Phylum Chaetognatha. Elongated, to a few centimeters, transparent, unsegmented coelomate invertebrate marine animals with a marked head, trunk, and tail. The head bears eyes, chitin's spines, and jaws. They arecarnivours. The trunk and tail have lateral and caudal fins. The alimentary canal is straightened simple, there is no special excretory, respiratory, or vascular system. Arrow worms are cross-fertilizing hermaphrodites without a larval stage. They are very common and abundant and some species are characteristic for certain water masses.