saddle oyster vs Anomia ephippium

saddle oyster and Anomia ephippium both are nouns.

Word	Noun	Adjective	Verb	Adverb
saddle oyster	Yes	No	No	No
Anomia ephippium	Yes	No	No	No

As nouns, saddle oyster and Anomia ephippium are synonyms defined as:

saddle oyster and Anomia ephippium: thin-shelled bivalve having the right valve deeply notched

saddle oyster (noun)	Anomia ephippium (noun)
thin-shelled bivalve having the right valve deeply notched	thin-shelled bivalve having the right valve deeply notched