Protists are a diverse group of eukaryotic organisms that are not classified as animals, plants, or fungi. They have simple cellular organization without specialized tissues or organs. Protists range from unicellular organisms like amoebas to multicellular forms like seaweed. Though diverse in appearance, protists are grouped together in the Kingdom Protista because they do not fit into other kingdoms. There are estimated to be between 60,000 to 200,000 protist species.