The next few exercises will concern members of the kingdom Protista. Under the five-kingdom classification, the Protista remain the most difficult to define and characterize. During the past 10 years, those interested in classification have intensified their efforts to validate a generally acceptable taxonomic plan. These attempts have been hindered, in part, by the fact that the groups being considered have traditionally been dealt with by different groups of biologists. Zoologists have been concerned with the "animal-like" protists and botanists with the "plant-like" protists. The most successful efforts to characterize the Protista have come from the views: 1) the protista are unicellular, eukaryotic organisms or 2) the protista are eukaryotic organisms without the development of clearly differentiated tissues. Neither of these two views appears to be totally acceptable because it is clear that the Protista represent a group with polyphyletic origins. Chapter 28 of Campbell introduces some recent attempts to make order of the Protista, and we will refer back to these new classifications from time to time. We will use a more traditional approach to introduce some of the Protista, one that considers the mode of nutrition. Autotrophic protists (those that undergo photosynthesis) have been traditionally grouped together as the “algae,” and we will review the algae in one lab. Some protists obtain their nutrition by absorption of food, like fungi. These fungal-like protists will be considered with the fungi in a later lab. The protists that obtain their nutrition heterotrophically by ingestion, like animals, have been traditionally considered the “protozoa.” These are the subject of today’s lab. While we know that the protozoa do not constitute a monophyletic group, we will learn about the kinds of heterotrophic protists today: who they are, how they are constructed, and how they live.

In today's exercise we will examine representative types of heterotrophic protozoa. Phylum Rhizopoda (amoebae) is represented by both free-living and symbiotic forms. Phylum Kinetoplastida contains some specialized flagellated protozoa. Phylum Foraminifera consists of marine organisms characterized by pore-studded shells composed of calcium carbonate (“chalk”) that surround an amoeba-like cell. Phylum Actinopoda includes those marine organisms known as radiolarians. Phylum Apicomplexa are all symbiotic (usually parasitic) and is represented by some 5,000 described species including the malarial parasite Plasmodium. They belong to the same kingdom (Alveolata) as the Ciliophora and the dinoflagellates. Phylum Ciliophora is perhaps the most familiar to you and includes the first microbes seen by Anton van Leeuwenhoek in 1673. There are 8,000 described species with Paramecium being the most familiar genus and perhaps one of the most commonly found protists of lakes and ponds. Ciliates are perhaps the most complex unicellular organisms.

• Phylum Rhizopoda
• Foraminiferans and Radiolarians
• Flagellated Protozoa
• Phylum Apicomplexa
• Phylum Ciliophora

Summary

Other than their unicellular, eukaryotic nature, what comments can you make about the diversity of these protozoa? Are they very similar to one another? Comment on their size, shape, structure, and life style. Large, multicellular organisms usually have organ systems. These are often regarded in animal systems as skeleton, musculature, integument, circulation, respiration, excretory, digestive, nervous, endocrine, and reproductive systems. Which of these systems have you observed in the protozoa examined today, and what are the protozoan analogous systems? Which of these systems appear to be absent? Can you provide an explanation for their absence?