Arrowworm

arrowworm, also called chaetognath, any member of a group of free-living wormlike marine carnivores that belong to the invertebrate phylum Chaetognatha. The bodies of arrowworms appear transparent to translucent or opaque and are arrow shaped. There are more than 120 species, most of which are in the genus Sagitta. The size of arrowworms ranges from about 3 millimetres to more than 100 millimetres; species inhabiting colder waters generally are larger than those from tropical seas. Chaetognaths are simultaneous hermaphrodites (that is, each individual has both male and female sex organs, or gonads). The body is divided into head, trunk, and tail by two transverse walls or membranes and possesses paired lateral fins and a tail fin. Respiratory, circulatory, and excretory systems are not well developed.