What you’ll learn to do: Identify the common characteristics of protists
There are over 100,000 described living species of protists, and it is unclear how many undescribed species may exist. Since many protists live as commensals or parasites in other organisms and these relationships are often species-specific, there is a huge potential for protist diversity that matches the diversity of hosts. As the catchall term for eukaryotic organisms that are not animal, plant, or fungi, it is not surprising that very few characteristics are common to all protists.
Traditionally, protists were classified due to their size, shape and color. When Robert Whittaker proposed original Kingdom, he recognized that some members did not fit an easily identifiable mold. With the advent of genetic testing, the entire classification and description of this group has changed, resulting in new species and new genealogy.