Chaetognatha
From ZooTerms (Dictionary of Invertebrate Zoology)
phylum of free-living planktonic or benthic animals, commonly called arrowworms, having an elongated more or less translucent body with large grasping spines at the head and a posterior horizontal tail fin.
Chaetognatha also chaetognaths (noun, plural; Greek chaite, hair; gnathos, jaw): A