April 2012: Stentors are not rotifers
On pages 44 and 45 of Life on the Dock (LOTD) I display three images of animals that I claim are rotifers. However, they are almost certainly Stentors, a genus of unicellular organisms. Wikipedia says in their entry for Stentor: "…ring of prominent cilia around the anterior bell that sweep in food…". These animals do indeed have such a ring.
They are very common in fresh water, but some species are marine. They are some of the largest single cell organisms. Some are 1 millimeter long (remember a typical cell is 0.01 - 0.02 mm in diameter). The shape of a Stentor can change, since its cell wall is flexible, almost like an amoeba. Notice the bent shape of the animal on page 45 of LOTD. As I followed the animals I could see their shape occasionally change dramatically.
Rotifers also have a row of cilia around their anterior end, and use them to sweep food into their gut. However, rotifers (a phylum, not a genus) typically have 500-1000 cells, and the animal is covered by rigid plates. While the appendages of Rotifers can move, the body segments have a fairly constant shape. Thus, Rotifers are more like copepods than amoeba in structure.
I learned of the correct identification of the animals on pages 44 and 45 by way of an e-mail from Franz Neidl, who lives in the port town of Formia, Italy, and had purchased a copy of LOTD. Franz is one of many members of a group that posts images and articles on the Internet at two "sister" web sites:
While the correct identification of the animals on pages 44 and 45 of LOTD is very useful, I think knowing about these web sites is even more important for me and readers of LOTD. I have spent hours looking at the beautiful and instructive pictures on these sites. Thanks to Franz for the introduction!
Phase contrast microscopy
On page 143 of LOTD I made a rather severe reference to phase contrast: "High-end microscopes can cost more than $50,000, because they contain the best optical components and use sophisticated optics, such as phase contrast, florescence, etc."
In fact, it can be possible to add phase contrast to a microscope for a few hundred additional dollars. Of course if you prowl the used microscope market, you may find phase contrast for less than that. Phase contrast can certainly be very useful for small transparent organisms. There are two main kinds of phase contrast, and (surprise) the (often) more powerful is the more expensive. Go to Wikipedia to learn about phase contrast.