ascidian vs sea squirt

ascidian and sea squirt both are nouns.

Word	Noun	Adjective	Verb	Adverb
ascidian	Yes	No	No	No
sea squirt	Yes	No	No	No

As nouns, sea squirt is a hyponym of ascidian; that is, sea squirt is a word with a more specific, narrower meaning than ascidian:

ascidian: minute sedentary marine invertebrate having a saclike body with siphons through which water enters and leaves
sea squirt: ascidian that can contract its body and eject streams of water

ascidian (noun)	sea squirt (noun)
minute sedentary marine invertebrate having a saclike body with siphons through which water enters and leaves	ascidian that can contract its body and eject streams of water