Microbenthosnoun
(biology) benthic organisms that are less than .1 mm in size and thus microscopic.
Macrobenthosnoun
(biology) benthic organisms that are big enough to be seen with the naked eye
Macrobenthos
Macrobenthos consists of the organisms that live at the bottom of a water column and are visible to the naked eye. In some classification schemes, these organisms are larger than 1 mm; in another, the smallest dimension must be at least 0.5 mm.