ascidian vs urochordate

ascidian and urochordate both are nouns.

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

As nouns, urochordate is a hypernym of ascidian; that is, urochordate is a word with a broader meaning than ascidian:

ascidian: minute sedentary marine invertebrate having a saclike body with siphons through which water enters and leaves
urochordate: primitive marine animal having a saclike unsegmented body and a urochord that is conspicuous in the larva

Other hypernyms of ascidian include tunicate, urochord.

ascidian (noun)	urochordate (noun)
minute sedentary marine invertebrate having a saclike body with siphons through which water enters and leaves	primitive marine animal having a saclike unsegmented body and a urochord that is conspicuous in the larva