I thought I had seen all of the life in the aquarium at least once. I was wrong. The final round of observations this week turned up nearly all of the genera that have become familiar (limnias, difflugia, centropyxis, more centropyxis, dead centropyxis, cladophora, etc.), but also two species that had escaped notice so far.

The first was a species of cyclidium, a motile single cell ciliate, with a visible indentation on one side adjacent to its contractile vacuole (Patterson). With the aid of this vacuole, the cyclidium made abrupt, very rapid movements across the field of view. It took a few minutes to find one that held still long enough for indentification.

It is entirely possible that the cyclidium have been present in some numbrs since week one, but that is less likely for the second new organism observed this week. Dr. McFarland spotted a blob of a species of the colonial cyanobacterium gomphosphaeria (Forest). The individual greenish (photosynthetic) coccoid cells could be seen suspended in the mucilaginous sheath characteristic of cyanobacteria. The colonies of this organism may have only recently grown to a size great enough to be easily identifiable.

At week three I noted something of a decline in activity in the microaquarium. However, in the past two weeks that trend has reversed, suggesting that this tiny ecosystem might have been capable of sustaining itself for many more weeks to come.

This week in the micro-aquarium the variety  of organisms are much the same as last week, with a few exceptions. The relative numbers of the organisms continues to change, however. The diatoms, of several different species have exploded in number, recognizable by their small size and the yellow green refraction of light on their silica shells. 

The shelled amoebas have decreased in number, with the number of living approximately equal to the number of dead observed in the aquarium. The remains of centropyxis are especially numerous on the bottom layers of the water. 

Multiple species of algae continue to spread throughout the aquarium including the branched cladofora species identified last week, as well as an (unbranched) oedogonium species first spotted this week. In addition to the algae, the similarly filamentous cyanobacteria (also known as blue-green algae) oscillatoria and nodularia were observed this week. 

The elusive nematode (which I thought had died) made another appearance this week. It was observed tearing (feeding?) at some algal material with its mouth parts just above the soil layer at the bottom of the aquarium. 

Rounding out the observations this week were the previously documented protists limnias (multicellular), stentor (unicellular), and vorticella (unicellular) species, which continue to be amazing and strange. The highlight of this group this week was the vorticella, whose stalk was visible for the first time, attached to a filament of cladofora.

I missed the first two weeks, so this will be the first post from the aquarium.

As you can see from the gallery above, at week three there is still a great variety of life in the water. Compared to last week it seems there are fewer total organisms, but the diversity of life has, if anything, increased. The numbers of the fast moving Euchlanis rotifers present at week two have dropped precipitously, being replaced in part by a different, straight-toed rotifer species (above).

Similarly the numbers of shelled amoebas (like Difflugia) have decreased somewhat but stellate amoebas like the one pictured above are now numerous. As you can see in the background of most all of these images, chlorophyte algae that existed as colonies of only a few cells last week have now colonized the aquarium successfully, especially the branched Cladophora. Cyanobacteria are also now present. Unfortunately the wily nematode that I spotted in week two but was unable to photograph seems to have vanished.

The most striking thing under the microscope this week is the Stentor. This trumpet shaped organism is in the middle of a reproductive division as can be seen in the growth on the side of the trumpet above.

Thanks to Dr. McFarland for help identifying all these crazy things.

Bibliography

Bibliography:

Forest, Herman S. Handbook of Algae: With Special Reference to Tennessee and the Southeastern United States. Knoxville, TN. University of Tennessee Press.

http://botany1112014.blogspot.com

Patterson, David J. Free-living Freshwater Protozoa: a Colour Guide. New York: Wiley, 1996. Print.

Pennak, Robert W. Fresh-water Invertebrates of the United States: Protozoa to Mollusca. New York: Wiley, 1989. Print.

Prescott, G.W. 1978. How to Know Freshwater Algae. 2nd Edition. Dubuque, IA. W.C. Brown Publishing. 

Are we inside the microaquarium of some much larger life form? No, probably not.