( ( ( Benthos and ) benthic ) ( ( refers ( to ( ( living ( ( ( on or ) under ) substrate ) ) ( at ( ( the bottom ) ( of ( the ocean ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Benthos) (CC and) (NN benthic)) (VP (VBZ refers) (PP (TO to) (S (VP (VBG living) (PP (IN on) (CC or) (IN under) (NP (NN substrate))) (PP (IN at) (NP (NP (DT the) (NN bottom)) (PP (IN of) (NP (DT the) (NN ocean))))))))) (. .)))
Benthos and benthic refers to living on or under substrate at the bottom of the ocean.
(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.