What are microscopic animals in the ocean/water called?

 In an aqueous environment, microscopic animals and plants are collectively known as plankton.

Plankton which can do photosynthesis are called phytoplankton, examples of which include diatoms, dinoflagellates, algae etc.,

Plankton which feed on phytoplankton are called zooplankton, examples of which include protozoans and larvae of animals.

'Protists' is the general term for single-celled organisms, including phytoplankton and protozoa.

Question by: Anunandha K M, VIII C