Biological Diversity Classified
Kingdom Protista
 
Note: there are certain fungus-like organisms and large, plant-like algae that are now, for cladistic (refer to lecture) reasons, usually considered in this kingdom. In spite of their likely phylogenetic relationships, we will follow a more traditional approach because of their visible traits. Look for the Oomycota with the fungi and the Chlorophyta, Phaeophyta and Rhodophyta with the plants. Still, there are well over a dozen phylum-level groups within this kingdom; we consider only a fraction of these. They all share the characteristics of eukaryotic cells that occur singly or occasionally colonially.
 

Algal-like protists

These quite different organisms share the traits of being unicellular (occasionally colonial), aquatic and photosynthetic. They almost certainly are unrelated evolutionarily, however similar ecologically.

 

            Phylum Bacillariophyta These cells possess chlorophyll a and c, other, yellow-brown, pigments, and double shells containing silica. An example is:                         diatoms These organisms are either elongate (bilateral symmetry) or with radial symmetry.               Phylum Dinoflagellata (Pyrrophyta) These cells possess chlorophyll a and c, two flagella, and a shell of cellulose plates. An example is:                         Ceratium These organisms have several points or horns to their shells; flagella are not very obvious.

 

 Phylum Euglenophyta These cells have no cell wall (although they do generally have a definite, though flexible, shape), chlorophyll a and b, and possess a flagellum or two. An example is:                         Euglena The flagellum, which is difficult to see, pulls the cell through the water like a propeller; some forms are heterotrophic.

 

 Fungus-like protists: the Slime Molds
  There are at least two unrelated groups of organisms that are more like the fungi than any other group of multi-cellular organisms, but actually have some characteristics of organisms in each of the multi-cellular kingdoms. Since we do not have the material to distinguish these in laboratory, we will just consider this group of organisms as Slime Molds. An example is:

    Ceratiomyxa
 

This organism shows both cytoplasmic streaming (frozen in this preserved specimen) and spore production. Note the pseudopod-like extensions of cytoplasm and the tiny spores scattered on its surface.           Protozoa (the animal-like protists) All were once considered fairly closely related because of their clear animal-like traits (motility, e.g.), they are currently considered to exhibit widely varied levels of relatedness. In spite of the possible lack of phylogenetic closeness, they do share such characteristics as heterotrophy (mostly via ingestion of nutrients) and motility; many are rather complex and possess real behaviors.
       Phylum Zoomastigina
  The feature that is most distinctive is the flagellum, given their eukaryotic condition and absence of chloroplasts. Flagella are frequently relatively long and few in number, but are best distinguished by how they move the cell: either pulling the cell by a propeller-like movement near the tip, or pushing the cell like the tail of a tadpole or sperm cell. Examples are:       Trichonympha
  These organisms (Y) have many long flagella; they are mutualists in the guts of termites and related insects, digesting the cellulose that has been eaten. The slide is a smear of termite gut contents.                         Trypanosoma These organisms have a single flagellum held against the cell by a membrane; they are blood parasites transmitted among species of birds or mammals by tsetse flies. The slide is a blood smear; note RBC (R), WBC (W) and trypanosomes (T).

 

     Phylum Rhizopoda (Sarcodina) The distinctive feature for this group of protozoans is the use of pseudopods for locomotion; pseudopods are lobes of cytoplasm that push out from the body of the cell. Some species possess tests (tiny shells), but the cells themselves have no fixed shape. Examples are:                     Amoeba This organism is fairly large for a single cell. It has an obvious nucleus (N) and pseudopods (P); vacuoles (V) are often visible, and the cytoplasm appears grainy.                     Foraminifera These organisms, which capture food and locomote using pseudopods, are most easily distinguished by their tests, which are bilaterally symmetrical and often resemble tiny snail shells. The slide is of empty shells.

 

             Phylum Sporozoa This group consists entirely of endoparasites, which have no locomotor structures and frequently reproduce via multiple fission and a complex life cycle. An example is:                         Eimeria This is a gut parasite of mammals. The slide shows numerous parasite cells (E) in the gut lining (G).               Phylum Ciliophora This is the largest group of protozoans; they are clearly the most complex structurally, and probably behaviorally as well. They are distinguished by the presence of cilia, which are frequently relatively short and abundant; cilia are best distinguished by their mode of action which is oar-like on the power stroke and limp on the recovery stroke. They also possess complex nuclei. Examples are:                         Stentor This is a filter-feeding ciliate, which generally feeds attached to the substrate in a funnel-shaped form, but can release from the substrate and adopt various forms to swim to another locale. It has a large, segmented nucleus, which looks like a string of beads (N).                         Didinium This is a one-celled predator (D)! They feed on paramecium, (P) which are typically larger than themselves; after attacking, they swallow them whole. They have a large, ribbon-shaped nucleus and their cilia are restricted to a few bands.                         Paramecium Shaped something like a slipper footprint, these are entirely covered with cilia. They have one macronucleus (N) and two or more micronuclei; the latter are exchanged during conjugation - their form of sexual reproduction. Two different slides of this critter demonstrate both fission (asexual) and conjugation (sexual). A paramecium undergoing fission shows the transverse fission plane (F) and dividing nucleus (N). Two pairs of paramecium are engaged in conjugation.