seasnail vs moon shell

seasnail and moon shell both are nouns.

Word	Noun	Adjective	Verb	Adverb
seasnail	Yes	No	No	No
moon shell	Yes	No	No	No

As nouns, moon shell is a hyponym of seasnail; that is, moon shell is a word with a more specific, narrower meaning than seasnail:

seasnail: any of several creeping marine gastropods with a spirally coiled shell: whelks, tritons, moon shells, neritids
moon shell: marine gastropods having smooth rounded shells that form short spires

Other hyponyms of seasnail include neritid, neritid gastropod, whelk, triton, moonshell, periwinkle, winkle, limpet.

seasnail (noun)	moon shell (noun)
small tadpole-shaped cold-water fishes with pelvic fins forming a sucker; related to lumpfish	marine gastropods having smooth rounded shells that form short spires
any of several creeping marine gastropods with a spirally coiled shell: whelks, tritons, moon shells, neritids