In the five-kingdom classification of biological organisms, a kingdom within the superkingdom Eukarya. Protoctists are aquatic eukaryotes, but they are not plants, animals, nor fungi. The kingdom includes naked and shelled amoebae, the Foraminiferida, zooflagellates, ciliates, Dinophyceae, Bacillariophyceae, all algae (see alga), protozoa, slime moulds, and slime nets. The name is not used in the three-domain classification, the protoctists being placed in other kingdoms in the domain Eukarya.