urochordate vs doliolum

urochordate and doliolum both are nouns.

Word	Noun	Adjective	Verb	Adverb
urochordate	Yes	No	No	No
doliolum	Yes	No	No	No

As nouns, doliolum is a hyponym of urochordate; that is, doliolum is a word with a more specific, narrower meaning than urochordate:

urochordate: primitive marine animal having a saclike unsegmented body and a urochord that is conspicuous in the larva
doliolum: free-swimming oceanic tunicate with a barrel-shaped transparent body

Other hyponyms of urochordate include ascidian, salp, salpa, larvacean, appendicularia.

urochordate (noun)	doliolum (noun)
primitive marine animal having a saclike unsegmented body and a urochord that is conspicuous in the larva	free-swimming oceanic tunicate with a barrel-shaped transparent body