ophidian vs sea snake

ophidian and sea snake both are nouns.

Word	Noun	Adjective	Verb	Adverb
ophidian	Yes	No	No	No
sea snake	Yes	No	No	No

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

ophidian: limbless scaly elongate reptile; some are venomous
sea snake: any of numerous venomous aquatic viviparous snakes having a fin-like tail; of warm littoral seas; feed on fish which they immobilize with quick-acting venom

Other hyponyms of ophidian include colubrid, colubrid snake, blind snake, worm snake, constrictor, elapid, elapid snake, viper.

ophidian (noun)	sea snake (noun)
limbless scaly elongate reptile; some are venomous	any of numerous venomous aquatic viviparous snakes having a fin-like tail; of warm littoral seas; feed on fish which they immobilize with quick-acting venom