Kingdom Protista: Protozoans

The Following Protists Are Often Included In Zoology Courses
They Are Placed In Phyla Rather Than Divisions By Zoologists:

    1. Phylum Sporozoa (Parasitic Protozoans): e.g. malaria
    2. Phylum Ciliophora (Ciliated Protozoans): e.g. paramecia
    3. Phylum Rhizopoda (Amoeboid Protozoans): e.g. amoeba

4. Phylum Zoomastigophora (Flagellate Protozoans): e.g. trypanosomes

1. Phylum Sporozoa

Sporozoans are nonmotile, unicellular protists which are commonly parasitic on vertebrate animals. Probably the best known sporozoan is Plasmodium vivax and three additional species, the one-celled organisms that cause malaria. The microorganisms invade red blood cells where they multiply, eventually escaping from the ruptured cells. The disease is characterized by spells of fever and chills, associated with the simultaneous rupture of red blood cells. Malaria is certainly one of the most widespread diseases throughout tropical regions of the world, and it is transmitted through the bite (blood meal) of the female Anopheles mosquito. During the 1600s, Spanish Jesuits in Lima, Peru learned that bark extracts from a local tree in the coffee family (Rubiaceae) called "quina" (Cinchona officinalis) could cure malaria. [Later it was discovered that this "extract" contained the quinoline alkaloid called quinine.] They successfully used this extract on Countess Chinchon. According to O. Tippo and W.L. Stern (Humanistic Botany, 1977), the genus was named by Linnaeus in honor of the countess, but spelled it Cinchona rather than "Chinchona.". Today, quinine trees (C. ledgeriana) are grown in plantations, although many synthetic antimalarial drugs have been developed, such as atabrine, chloroquine and primaquine. Some strains of Plasmodium are resistant to many of the synthetic quinine analogues, so natural quinine is still used to this day. In fact, some people take prophylactic doses of bitter quinine water (tonic) in the evenings, usually mixed with gin or vodka.

2. Phylum Ciliophora

Magnified view (1000 X) of two individuals of Paramecium bursaria in their conjugating position. The cells are fringed with minute, hairlike cilia which propel them through the water. Each cell has a large macronucleus and a smaller micronucleus. Conjugation is a form of sexual reproduction in which the individual cells fuse together and swap nuclear DNA in the form of small micronuclei. Conjugation is unlike the fusion of gametes in other protists and animals. It involves the division and fusion of micronuclei from opposite paramecia. After conjugation each paramecium continues on its way, genetically altered from its brief encounter because of different chromosomal combinations. The genetically altered paramecia continue to produce clones of themselves by asexual cell division, a process known as fission. [Image from an old (circa 1960) prepared microscope slide enhanced with Adobe PhotoShop by W.P. Armstrong.]

3. Phylum Rhizopoda (incl. Amoebozoa & Percolozoa)

Magnified view (1000 X) of an individual Amoeba proteus showing a faint nucleus and cytoplasmic extensions called pseudopodia. The jellylike protoplasm of the amoeba slowly moves in the direction of its flowing pseudopodia. The amoeba feeds on other protozoans and unicellular algae by engulfing them in its pseudopodia. This "cell eating" phenomenon (called phagocytosis) is also exibited by human white blood cells called phagocytes. The dreaded disease of travelers called amoebic dyssentary is caused by the parasitic Entamoeba histolytica that invades the digestive tract of humans. The disease is spread by fecal contamination of drinking water, raw vegetables and careless food handlers. [Image from an old (circa 1960) prepared microscope slide enhanced with Adobe PhotoShop by W.P. Armstrong.] Note: Some references place this species in the phylum Amoebozoa.

Another interesting amoeboid protozooan (Naegleria fowleri) occurs in the water and mud of warm freshwater bodies, such as lakes, rivers, and geothermal hot springs, especially during the summer months with warm ambient air tempatures and lower water levels. Although only 23 infections have been documented in the U.S. between 1995 and 2004, this amoeboid protozoan causes a fatal disease called Primary Amoebic Meningoencephalitis (PAM) that results in destruction of the brain tissue. Scientists predict that the frequency of this disease will increase with global warming. The amoeba enters the body through the nose, generally when people are swimming or playing in warm water where the water goes up the nostrils. The ameba penetrates the olfactory mucosa and nasal tissues where it causes necrosis and hemorrhaging. From here it climbs along nerve fibers through the floor of the cranium and into the brain. This amoeba has been found across the southern United States, including Florida, Texas and Lake Havasu on the Colorado River between California and Arizona. Although infections with this microorganism are rare, two suggested preventage measures are to avoid warm, standing water known to contain these organisms and always wear good nose plugs. Note: Some references place this species in the phylum Percolozoa because it can transform between amoeboid, flagellate and encysted stages.

4. Phylum Zoomastigophora

Highly magnified view (2000 X) of Trypanosoma lewisi (red arrow) swimming among red blood cells of a rat. Several species of Trypanosoma infect humans. African sleeping sickness is caused by T. gambiense and T. rhodesiense, two species of flagellates transmitted by biting flies of the genus Glossina, better known as tsetse flies. Unless treated in early stages, African sleeping sickness is a potentially fatal disease. Chagas disease of the American tropics is caused by another trypanosome (T. cruzi) that is spread by blood-sucking bugs of the genera Triatoma and Rhodnius. In the southwestern United States, a species of Triatoma called the cone-nosed bug (T. protracta) inhabits the nests of wood rats (Neotoma spp.). Using their piercing mouthparts, these bugs primarily suck the blood of wood rats. They are known to carry a trypanosome and occasionally bite people while they are sleeping. Symptoms of the bite range from mild itching, severe joint pain, nausea, chills and dizziness to anaphylactic shock. Most people exibit no adverse reactions, and the severe cases reported in hypersensitive people appear to be due to serious allergic reactions, possibly from the bug's saliva. [Image from an old (circa 1960) prepared microscope slide enhanced with Adobe PhotoShop by W.P. Armstrong.]

A wood rat nest (black arrow) in the coastal sage scrub plant community east of Palomar College. The nest is constructed by the dusky-footed wood rat (Neotoma fuscipes). It is made of sticks and dead branches, mostly from sagebrush (Artemisia californica) and black sage (Salvia mellifera). In the southwestern United States, the cone-nosed bug (Triatoma protracta) inhabits the nests of wood rats. Using their piercing mouthparts, these bugs primarily suck the blood of Neotoma species. They are known to carry a trypanosome and occasionally bite people while they are sleeping. Because they typically bite in soft areas of the body, such as the lips, they are sometimes called "kissing bugs."

The western cone-nosed bug (Triatoma protracta) inhabits the nests of wood rats in the southwestern United States. Using their piercing beak, these bugs primarily suck the blood of Neotoma species. They are known to carry a trypanosome and occasionally bite people while they are sleeping. Because they typically bite in soft areas of the body, such as the lips, they are sometimes called "kissing bugs." Cone-nosed bugs belong to the Reduviidae, a family of predatory bugs with elongate, tapering snouts.

Drawing of highly magnified view (2000x) of brine from Owens Salt Lake, California showing rod-shaped, salt-loving bacteria (Halobacterium) and two species of flagellated halophilic green algae, including Dunaliella salina (upper left) and Dangeardinella saltitrix (lower right) swimming among cuboidal crystals of sodium chloride. The latter species has a smaller, slender, pear-shaped cell with two peculiar flagella, one extending forward and one trailing behind. A single drop of brine may contain literally millions of the minute bacteria. [Illustration Courtesy Of Graphic Artist Elaine M. Collins.]

References

Barnes, R.D. 1980. Invertebrate Zoology. W. B. Saunders Company, Philadelphia.
Borror, D.J. and D.M. DeLong. 1964. An Introduction To The Study Of Insects. Holt, Rinehart & Winston, New York.
Hogue, C.L. 1993. Insects of the Los Angeles Basin. Natural History Museum of Los Angeles County, Los Angeles, California.
Jessop, N.M. 1988. Zoology (Schaum's Outline Series). McGraw-Hill Book Company, New York.
Margulis, L., K.V. Schwartz, and M. Dolan. 1994. The Illustrated Five Kingdoms: A Guide To The Diversity Of Life On Earth. HarperCollins College Publishers, New York.
Storer, T.I. and R.L. Usinger. 1957. General Zoology. McGraw-Hill Book Company, Inc., New York.

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