Phylum Chaetognatha

Arrow worms are a small group of almost strictly planktonic marine animals. They are characterized externally by a group of bristle like jaws on each side of the mouth, a pair of eye spots on the back of their head, a horizontal tail fin, and two pairs of lateral fins. (Kozloff, 2000)

References:

Brusca, R.C., and Brusca, G.J. (2003). Invertebrates. Library of Congress Catologing-in-Publication-Data: USA.

Kozloff, Eugene N. (2000). Seashore Life of the Northern Pacific Coast. University of Washington Press: Seattle and London.