Protists are generally defined by what they are not than by what they ARE. They are not monophyletic clades, they do not belong in other eukaryotic kingdoms, they contain much more diversity. They can exist as algae, protozoan, absorptive, forms. As well as photoautotrophs, chemoheterotrophs, and mixotrophs. They are extremely diverse in terms of form, nutrition, and asexual reproduction. So what is their distinguishing trait? What differentiates them and why are they defined in this matter? It is somewhat vague that they are described by what they are not than by what they are.