Benthic /Benthos are an Organism that feeds on the sediment at the bottom of a water body such as an ocean, lake, or river.

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Other /More definition:
Benthos are animals without backbones, living in or on the sediments, a size large enough to be seen by the unaided eye, and which can be retained by a U.S. Standard No. 30 sieve (28 openings/inch, 0.595-mm openings). Also referred to as bentic macroinvertebrates, infauna, or macroBenthos.