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. As a hobbyist definition, specific gravity is the amount of salt in the water. See the hydrometer definition above for more information. Specific Gravity of seawater ranges from 1.022 to 1.030. The most famous example is the clownfish and the anemone.