* Unicellular plankton: This includes single-celled organisms like diatoms, dinoflagellates, and some bacteria. These are often referred to as phytoplankton.

* Multicellular plankton: This includes larger organisms like jellyfish, krill, and some types of algae. These are often referred to as zooplankton.

Therefore, plankton is a term that encompasses both unicellular and multicellular organisms.