sagitta vs chaetognath

sagitta and chaetognath both are nouns.

Word	Noun	Adjective	Verb	Adverb
sagitta	Yes	No	No	No
chaetognath	Yes	No	No	No

As nouns, chaetognath is a hypernym of sagitta; that is, chaetognath is a word with a broader meaning than sagitta:

sagitta: any arrowworm of the genus Sagitta
chaetognath: any worm of the Chaetognatha; transparent marine worm with horizontal lateral and caudal fins and a row of movable curved spines at each side of the mouth

Other hypernyms of sagitta include arrowworm.

sagitta (noun)	chaetognath (noun)
any arrowworm of the genus Sagitta	any worm of the Chaetognatha; transparent marine worm with horizontal lateral and caudal fins and a row of movable curved spines at each side of the mouth