neritid gastropod vs seasnail

neritid gastropod and seasnail both are nouns.

Word	Noun	Adjective	Verb	Adverb
neritid gastropod	Yes	No	No	No
seasnail	Yes	No	No	No

As nouns, seasnail is a hypernym of neritid gastropod; that is, seasnail is a word with a broader meaning than neritid gastropod:

neritid gastropod: operculate seasnail of coastal waters with a short spiral shell
seasnail: any of several creeping marine gastropods with a spirally coiled shell: whelks, tritons, moon shells, neritids

neritid gastropod (noun)	seasnail (noun)
operculate seasnail of coastal waters with a short spiral shell	small tadpole-shaped cold-water fishes with pelvic fins forming a sucker; related to lumpfish
	any of several creeping marine gastropods with a spirally coiled shell: whelks, tritons, moon shells, neritids