benthos vs merobenthos

benthos and merobenthos both are nouns.

Word	Noun	Adjective	Verb	Adverb
benthos	Yes	No	No	No
merobenthos	Yes	No	No	No

As nouns, merobenthos is a hyponym of benthos; that is, merobenthos is a word with a more specific, narrower meaning than benthos:

benthos: organisms (plants and animals) that live at or near the bottom of a sea, lake, river or stream
merobenthos: benthos consisting of organisms in pre-adult stages that later become adult in the plankton.

Other hyponyms of benthos include marine benthos, epipsammon, endopsammon, epixylon, epipelon, microbenthos.

benthos (noun)	merobenthos (noun)
organisms (plants and animals) that live at or near the bottom of a sea, lake, river or stream	benthos consisting of organisms in pre-adult stages that later become adult in the plankton.
a region including the bottom of the sea and the littoral zones