merino sheep vs Ovis aries

merino sheep and Ovis aries both are nouns.

Word	Noun	Adjective	Verb	Adverb
merino sheep	Yes	No	No	No
Ovis aries	Yes	No	No	No

As nouns, Ovis aries is a hypernym of merino sheep; that is, Ovis aries is a word with a broader meaning than merino sheep:

merino sheep: white sheep originating in Spain and producing a heavy fleece of exceptional quality
Ovis aries: any of various breeds raised for wool or edible meat or skin

Other hypernyms of merino sheep include domestic sheep.

merino sheep (noun)	Ovis aries (noun)
white sheep originating in Spain and producing a heavy fleece of exceptional quality	any of various breeds raised for wool or edible meat or skin