Traditionally divided into protozoans (“primitive animals”) and algae (“primitive plants”), protists are a grab-bag of different organisms. Simply put, they comprise all the eukaryotes except for plants, animals, and fungi.
- Eukaryotes. These are cells that have a membrane-bound nucleus. This means that bacteria are not protists.
- Mostly unicellular. Plants, animals, and fungi are the classic examples of multicellular organisms. Most protists are single-celled organisms, but many are not. Examples of multicellular protists include the algae. Some can reach huge sizes, such the giant kelp.
- Not a “natural” grouping. The standard for biological classification is the monophyletic group – a group that is (i) descended from a common ancestor and (ii) that includes all its descendants. The protists violate the second of these requirements and is hence a paraphyletic group.
- Fun and fascinating. They swim, they spin, they jump, some even fly! (Okay, I’m stretching the truth a bit. Some have spores which drift through the air.)