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.