seasnail vs periwinkle

seasnail and periwinkle both are nouns.

Word	Noun	Adjective	Verb	Adverb
seasnail	Yes	No	No	No
periwinkle	Yes	No	No	No

As nouns, periwinkle is a hyponym of seasnail; that is, periwinkle 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
periwinkle: edible marine gastropod

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

seasnail (noun)	periwinkle (noun)
small tadpole-shaped cold-water fishes with pelvic fins forming a sucker; related to lumpfish	edible marine gastropod
any of several creeping marine gastropods with a spirally coiled shell: whelks, tritons, moon shells, neritids	small edible marine snail; steamed in wine or baked
	chiefly trailing poisonous plants with blue flowers
	commonly cultivated Old World woody herb having large pinkish to red flowers