( ( The benthos ) ( ( is ( ( an aggregation ) ( of ( organisms ( living ( ( ( on or ) at ) ( ( the bottom ) ( of ( ( a body ) ( of water ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NNS benthos)) (VP (VBZ is) (NP (NP (DT an) (NN aggregation)) (PP (IN of) (NP (NP (NNS organisms)) (VP (VBG living) (PP (IN on) (CC or) (IN at) (NP (NP (DT the) (NN bottom)) (PP (IN of) (NP (NP (DT a) (NN body)) (PP (IN of) (NP (NN water)))))))))))) (. .)))
The benthos is an aggregation of organisms living on or at the bottom of a body of water.
(ROOT (S (NP (NP (VBG Living) (NNS things)) (PP (IN on) (NP (DT the) (NN ocean) (NN floor)))) (VP (VBP are) (VP (VBN known) (PP (IN as) (NP (NNS benthos))))) (. .)))
Living things on the ocean floor are known as benthos.