urochordate vs ascidian

urochordate and ascidian both are nouns.

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

As nouns, ascidian is a hyponym of urochordate; that is, ascidian 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
ascidian: minute sedentary marine invertebrate having a saclike body with siphons through which water enters and leaves

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

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