What kind of animal is plankton from spongebob?

Krill are planktonic crustaceans found worldwide. If you are not aware, plankton is not a species but a collective term with a specified definition covering many organisms. It is not a specific description of any one animal, any animal group, or indeed even restricted to describing animals at all. It is a definition that covers ANY organism living in water that is subject to any currents or other forms of movement that carry them