any small marine invertebrate of the genus Sagitta, having an elongated transparent body with fins and prehensile oral bristles: phylum Chaetognatha (chaetognaths)
arrowworm in American English
(ˈæroʊˌwɜrm; ˈɛroʊˌwɜrm)
noun
any of a phylum (Chaetognatha) of small, wormlike marine animals with an arrow-shaped,finned, almost completely transparent body: they feed on plankton