Invertebrate Zoology "protists"


Protists have captured the fancy of biologists since Leeuwenhoek first observed them (most of the "animalcules" he wrote about were protists). Like Leeuwenhoek, many people find protists inherently interesting, and biologists have learned much about life processes from protists. I hope that you will enjoy looking at a variety of these organisms in lab.

The kingdom Protista was first proposed in 1969 by Robert Whitaker to include all unicellular eukaryotic organisms. As research with protists progressed, biologists realized that protists have such a diversity of ultrastructure, life cycles, lifestyles, mitochondria, DNA sequence data, and evolutionary lineages, they cannot be put into a single kingdom. As a result, in the classification scheme recently accepted by most protozoologists, there is no longer a formal taxonomic category called the Kingdom Protista, although "protists" still serves as a useful term for referring to this large, diverse group of unicellular eukaryotes. In this course, our main purpose is to illustrate biological diversity and de-emphasize taxonomy. In order to avoid taxonomic problems, we'll group protists according to the kingdom of macroscopic organisms (plant, animal, or fungi) they most resemble; in other words, we will refer to protists that resemble plants (algae), protists that resemble fungi (slime molds), and protists that resemble animals (protozoa). The only protists that we will cover in detail this semester are the animal-like group commonly called the protozoa (another informal grouping).

The fossil record indicates that virtually all protist and animal phyla living today were present during the Cambrian period, about 550 million years ago. Unfortunately, fossil evidence of the evolutionary pathways that gave rise to these phyla is scarce. Instead, scientists gather evidence by examining the structure and function of living species.


1. Protists probably arose from several ancestral Archaean groups (Archea were the first living organisms on this planet).

2. Protists are unicellular (sometimes colonial) and eukaryotic (cells that have true nuclei and membrane-enclosed organelles).

3. Although most protists are microscopic, they vary in diameter from 5 micrometers to 5 millimeters

4. Some protists are plant-like, some fungus-like, some animal-like.*
*This course covers the animal-like protists = "protozoa" .


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