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.