Benthos and benthic refers to living on or under substrate at the bottom of the ocean. Sessile means the organism is attached to the substrate. The process by which organisms, usually plants, use the energy contained in light, usually sunlight. Although they may have some form of locomotion they are mostly carried by water currents. The microplankton is divided into zooplankton, tiny marine animals, and phytoplankton, or plants.
Most fish start their lives as small animals in the plankton.
A polyp is the living unit of a coral. For example, an amoeba. Pelagic refers to living in the water of the ocean above the bottom. Pelagic organisms have the ability to move around. Benthos and benthic refers to living near or under substrate at the bottom of the ocean.