urochord vs doliolum

urochord and doliolum both are nouns.

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

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

urochord: 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 urochord include ascidian, salp, salpa, larvacean, appendicularia.

urochord (noun)	doliolum (noun)
a notochord of a larval tunicate typically confined to the caudal region	free-swimming oceanic tunicate with a barrel-shaped transparent body
primitive marine animal having a saclike unsegmented body and a urochord that is conspicuous in the larva