If a eukaryote organism can't be classified as a fungi, plant, or animal; it is a member of the Protist kingdom of classification. Examples of protists are organisms like the single celled amoeba and kelp. Kelp aren't considered plants because they lack tissue that allows them to move water internally.
Unicellular or Multicellular
Protists can be either a single celled or multi-celled organism.
The cells that protists are made up of are complex. An important feature of eukaryote cells is that they contain a nucleus to safely protect and store genetic information.
Autotroph or Heterotroph
Some protist organisms use chloroplasts to produce their own energy. Protists are a diverse kingdom of organisms; some protists are able to produce their own food through photosynthesis while others rely on other organisms as food.