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At the end of the narrated portion of the DVD is a 15 minute observation section featuring additional protists of particular interest. This section is provided for teachers who would like to involve students in observing living protists, an activity that leads to discussion and research. It can be used as an introduction to the narrated stories, or played as “ambiance” during laboratory work with protists. One thing everyone agrees upon is that observing this remarkable footage of living microorganisms has tremendous learning benefits.

Five common Flagellated Protists

Opalina	Opalina showing many nucleii

Opalina: 100-200µ Although Opalina appears to be a ciliate, it is more closely related to certain flagellated organisms. Opalinids are intestinal parasite of amphibians. The species shown was taken from a tree frog tadpole. Note that Opalina is a multinucleated cell with hundreds of nuclei, a rare phenomenon in protists. Because most of the opalinid population occurs in the host�s rectum, Opalina is considered to be more commensal than a parasite.

To obtain opalinids for microscope study, without killing their host, use a glass eyedropper filled with 0.7% saline solution. The fire-polished end of the dropper can be gently inserted in the host�s cloaca. The idea is to provide a saline enema while sucking back a sample of the rectal content including any commensals it may contain. For a frog, the procedure may be a little unsettling, but certainly better than a postmortem extraction.

Questions: How might a multinucleated cell evolve? What kinds of nutrients are available to Opalina? How do tadpoles become infected?

Hexamita: around 20µ Hexamita is a diplomonad, related to Giardia, the notorious intestinal parasite known to travelers who indulge in untreated drinking water and spend the remainder of their trip in hospital bathrooms. The dark-field shot shows the typical rapid dancing behavior of unrestrained Hexamita. These came from a jar of putrid pond water in which a large freshwater bryozoan colony was decomposing (note the abundance of large spiral bacteria). Hexamita species are also common in the large intestine of frogs and salmonid fish.

Question: How might the transition from a free-living Hexamita to a parasite be accomplished? Might free living Hexamita have evolved the other way around--from parasite to free-living?

Dinobryon

Dinobryon: cells around 40µ Dinobryon colonies are found in the plankton of lakes. Colonial life may provide several advantages over living as a single isolated cell. Larger size may help prevent predation. Branching may help orient and stabilize the colony in the open water. Each new individual, resulting from division, builds on the rim of their sister and so derives all the benefits of colonial life.

Questions: Based on the video observation, in what group of protists would you place Dinobryon?

Codosiga on duckweed rootlet	Codosiga, collar and flagellum

Codosiga: cells around 20µ Choanoflagellates such as Codosiga live attached to other objects. The first scene shows a colony of Codosiga attached to a duckweed rootlet. These cells have transparent collars (seen in optical section). A long flagellum emerges from the collar where it creates food-trapping currents. Choanoflagellates are virtually identical to the collar cells of sponges, suggesting a close relationship. In fact, these little cells may be our closest living protistan relative.

Questions: What steps might a colonial choanoflagellate have undergone in becoming a sponge-like organism?

Gymnodinium, a dinoflagellate

Gymnodinium: around 40µ Gymnodinium is a common dinoflagellate found in lakes and ponds. The cells have a thin cellulose shell and two flagella. One flagellum is contained in a groove that circles the cell and produces rotation. The other flagellum projects posteriorly and provides forward locomotion. A surprising new finding, based on genetic analysis, is that dinoflagellates are more closely related to ciliates than to other flagellated protists.

Four “Unknowns” to identify:

#1 Ceratium is a dinoflagellate common in the plankton of lake, ponds and oceans. How might Ceratium�s structure be adaptive for planktonic life?
#2 Actinocystis is a colonial flagellate that produces a branching extension tube. The colonies break off and sheds individual cells which may start up new colonies. What advantages might gained by producing an extension?
#3 Phacus is a green flagellate with many species, some twisted, some flat. To what group of flagellates might Phacus be related?
#4 Synura is a colonial flagellate. Spherical colonies of flagellated cells are common in both the green and yellow-brown lines of life--and there are a few clear ones as well such as Actinocystis, #2 above.

Five Common Amoeboid Protists

Pelomyxa: 100-600µ These giant amoebas seldom put out pseudopods, creeping along by means of cytoplasmic waves. The one shown does indeed extend a broad pseudopod, but this may be in response to the coverglass pressing down on the organism. Pelomyxa is one of the few eukaryotic organisms lacking mitochondria, the ATP producing organelles that supply energy for cell use. Pelomyxa’s energy needs are met by symbiotic bacteria living in its cytoplasm. Some of these aerobic symbionts can be seen in the clear zone at Pelomyxa’s advancing surface.

Question: In what ways might Pelomyxa be a model for the evolution of mitochondria?

Hydramoeba

Hydramoeba: around 150µ We had been filming Hydra’s feeding and reproductive behavior. Our subjects, which numbered in the hundreds, suddenly went into an obvious decline. They stopped eating the copepods we sent their way and their tentacles withered to nubs. The day after we first noticed the decline all but a few had simply vanished. Examining the remaining sickly Hydras showed them to be stuffed with parasitic amoebas which oozed out when the Hydra was pressed by the coverglass. Other amoebas clung to the sickly hydra�s tentacles and body wall. Higher magnification showed that in addition to feeding on endothelial cells, the amoebas were ingesting the hydra�s nematocysts‹the stinging cells used to capture prey.

Questions: At what stage in the evolution of multicellular organisms did they become hosts for unicellular parasites? How might such relationships begin? How can a parasite benefit by killing its host?

Vampyrella

Vampyrella: Named for its ability to enter and absorb the cytoplasm of algae cells, Vampyrella is an amazing find. Entering and emptying one cell in an algal filament, Vampyrella then moves to next and on down the line.

Question: Many filamentous algas (Spirogyra, Zygonema) produce a jelly-like coating. What evolutionary pressures might account for these jelly sheaths?

Raphidocystis: This small heliozoan is easily recognized by its two types of axiopodia, long axiopods with beads that move up and down the axiopod, and shorter processes with wineglass tips.

Choanocystis: This delicate heliozoan demonstrates the amazing ability of axiopods to repair themselves. The real-time observation shows how the microtubules that make up the axiopod quickly reassemble and repair the broken structure.

Two "unknowns" to identify.

#5 Acanthocystis, a heliozoan filled with symbiotic algae (Chlorella). The fork-tipped processes are distinctive for this genus.
#6 Thecamoeba, an amoeba with a thick pellicle that forms folds. These slow moving amoebas ingest filaments of cyanobacteria.

Twelve Additional Ciliated Protists

Homalozoon: 400µ These large ciliates have a “nose” filled with toxicysts used to stun and kill small ciliate prey. In the dark-field observation, the “nose” touches a small ciliate which immediately disintegrates. Homalozoon then expands its anterior end and engulfs the prey. Homalozoon is adapted for living on, and moving slowly over, surfaces. In a petri dish it is often difficult to dislodge the cell, which adheres to the glass surface.

Question: How would you describe Homalozoon�s ecological niche? How does it “stick” to surfaces?

Lembadion: 120µ Common in pond vegetation, Lembadion is a specialist at capturing small rapidly swimming ciliates such as Halteria. The cell is cupped, forming a large open cavity. On either side of the cavity are membrane flaps. When feeding, the flaps repeatedly open and close. Upon a chance encounter with a small ciliate, the flaps stay closed, preventing the prey from escaping.

Question: How might Lembadion’s unique feeding structure have evolved? Which organisms in this collection would you guess to be its closest relatives?

Blepharisma: 130-200µ common in pond water. Two species are shown. Most ciliates are colorless, except for the colored food items they have ingested. Blepharisma is the rare exception. Cultured in bright sunlight it may appear colorless, but most individuals found in the shady aquatic jungles of ponds are pink. Blepharisma has a feeding channel, lined on one side by a membranous veil that traps small organisms and direct them to its mouth. On the other side of the channel, tufts of long cilia, beating in waves, help steer small food organisms into the cytostome. The second species shown in the observation cultures algae in its cytoplasm, a kind of symbiosis practice by a number of other large ciliates.

Strobilidium gyrans: 40µ Think of it as an escaped airplane motor running at full throttle. A ring of extremely powerful fused cilia create a feeding current that brings bacteria and small algae cells to Strobilidium's centrally located cytostome. Strobilidium secretes a tether, allowing it to remain in choice feeding zones. The tether is produced from a “tail” projection covered with “teeth” that appear to be used to snip the tether, allowing the cell go shooting away should danger threaten or local conditions deteriorate. In terms of body length traveled over time Strobilidium may well be world’s fastest protist. Under full power it can exceed 150 body lengths per second, not bad for a cell 40 micrometers in length moving through a viscous medium. Strobilidium is commonly found in aquatic plant infusions and seems more at home in well oxygenated water than in putrid cultures. This may be due to the high oxygen demands imposed by its powerful ciliature--the propellers that create its long-reaching feeding currents, and its remarkable speed.

Question: What is the advantage of living on a tether?

Six "unknowns" to identify.

Lionotus 100-200µ. Lionotus can be distinguished from other elongated ciliates by having cilia restricted to the outer curve of its “neck”. The inside curve lacks cilia but is equipped with trichites distributed along the length of the cytostome--a long slit running along the slender neck. If you find a population of Lionotus, try to determine how it feeds and the kinds of food it goes after.