Neophyte upending diatoms

Diatoms can be frustrating. The inspired novice diatomist, me, journeys to an estuary to collect mud, hopefully well endowed with a variety of diatoms. Having collected this mud I return home with expectations. After several washings in tap water, four or more, to eliminate salt and an additional two with distilled water to eliminate suspended clay, the mud is now ready for the sedimentation procedure. The result of this sedimentation process is a 50ml beaker containing a small quantity of material made up of a great number of diatoms, at least that is what is anticipated.

Agitate the 50ml beaker bringing the contents into suspension then after a few seconds extract a small quantity with an eyedropper. Place a drop on a slide, add a drop or two of distilled water to spread the material, and place the slide on the microscope stage. Now a look into the eyepiece and a big smile, plenty of diatoms. Within the illuminated circle there are a good number of large cylindrical shaped diatoms which I immediately take to be the girdle view. Also, within this small world are what I take to be the valves of centric diatoms.

Now the frustration begins, which valve belongs to which girdle? There is enough difference in size and shape to make me think I have more than one species. So I consult with an old friend William C. Vinyard, 'Diatoms of North America'. I am now confident, maybe, that the valves belong to the genus Biddulphia but the girdles do not match those depicted? I think that if I find one or two in an oblique view I could then associate valve with girdle. Again and again, slide after slide, I tried and I never found the oblique view that would, as I came to believe, allow me to associate valve with girdle.

Like most microscope enthusiasts I have several samples and projects simultaneously in progress. I have a desire to make arranged slides and grand hopes of making type slides of diatoms. While in this pursuit that little voice from within spoke, ‘hey dummy, up-end one of the cylinders’, an awakening.

The tool I use, the manual manipulator or seeker, is a piece of dowel about five inches in length fitted with a paint brush bristle at one end. The tool is easy to manufacture. One paint brush bristle stretched tight and cut with a sharp instrument at about a 30 degree angle. A pin is used to place a dimple centered at one end of the dowel to receive the blunt end of the bristle. Insert the bristle into the dimple, add a little glue, wait for the glue to dry, and it's done.

There is one additional requirement and that is a dissecting or binocular microscope. This additional scope gives one ample freedom to work. I work at 45x and this is very good with bottom illumination. As you will see this is adequate for work on diatoms down to around 50µm, smaller if you’re a particularly skilled or a lucky individual.

Back to the 50ml beaker, drop on slide, slide to microscope stage, an adequate sample of cylinders. Slide to hot plate. Once dried, slide to binocular microscope. Now to try and stand the cylindrical diatom on end. The large cylinder was easy to pick up and then placed on a second slide positioned alongside the sample slide. This slide has a small circle drawn in the center and the cylinder is set within this circle. Now the fun, can I maneuver the diatom into an upright position? With surprisingly little effort, yes, it worked! It was as though the diatom said ‘lets get this over with’. Next trick was to transfer the slide and upended diatom to the compound microscope. Gently transfer the side, place it ever so gently onto the stage and with low power find the diatom within the circle, increase power. Yes, my cylinder was defiantly Bidduphlia!

With one success more diatoms would follow, some easy, some hard. I tangled with one little diatom valve that would only stand on end. No matter how I tried I could not get it to lie presenting the valve face. Eventually, in frustration, I released a heavy sigh and whoosh it was gone. Upending diatoms has proven to be an interesting activity. Has it eliminated all the frustrations, of course not, there will always be problems and hopefully interesting new solutions.

Fig. 1.

Figure 1 above is my nemesis— the cylinder, valve view and girdle view. The currently accepted name for this diatom is Pleurosira laevis (Ehrenberg) the synonym Biddulphia laevis Ehrenberg is no longer accepted. The valve measures 64µm high by 61µm wide and the girdles length is approximately 107µm. The diatom on the right may also be Pleurosira but I am not certain. A little more research is needed. Three views are presented the upper is the girdle and the lower two are oblique views of the valve. Difficult to stand this diatom on end given the valve shape. The girdle length as pictured is approximately 128µm.

Fig. 2.

In Fig. 2 two fossil diatoms are pictured. The diatom on the left, valve and girdle, is in older texts Biddulphia. The valve in long axis measures approximately 54µm and the length of the girdle as pictured measures approximately 83µm. Biddulphia according to algeBASE (http://www.algaebase.org/) is a "confused group of 'biddulphioid' forms" and states that some species "have been transferred to Odontella, Pleurosira, Biddulphiopsis". I am inclined to identify this diatom as Odontella but I may also be confused. The diatom on the right I thought when I first saw it was a pygmy Biddulphia because unlike most observed it was small. Turning this diatom on end was a pleasant surprise, it is Triceratium elegans (Greville) Grunow. Its girdle measures approximately 40µm in length and the valve is approximately 32µm.

Fig. 3.

The fossil diatom in Fig. 3. is of the genus Auliscus. I have not identified the species. The valve markings within this genus are quite variable. This image depicts the entire diatom, valve, girdle, girdle rotated approximately 180 degrees, and the opposite valve. The two valves though different are remarkably similar which is expected but nice to observe first hand. The difference in the two girdle views is interesting. The right girdle has unique markings something like a pot overflowing. In A. Schmidt's Diatom Atlas, plate 31, fig. 15, Auliscus pruinosus var. sansibarica Grunow is depicted in a stack or chain with this particular marking on each of the diatoms in alignment. This representation suggests the marking could have purpose? Diameter measures approximately 78µm.

Fig. 4.

Fig. 4. is another fossil diatom genus Stictodiscus. Pictured here is valve, two images of the girdle, one rotated approximately 180 degrees, and the opposite valve. The alignment markings found in Fig. 3 are not present on this diatom. The diameter measures a healthy 116µm.

Fig. 5.

I wondered what the reverse side of a valve would look like. Fig. 5 depicts a valve high focus, side view of the valve, and high focus of the reverse side of the same valve. This fossil diatom is Actinoptychus bismarckii Schmidt.The genus Actinoptychus is described as being comprised of six or more undulating sectors or compartments, valve diameter 135µm. The undulation is apparent in the side view of this valve. Using the notch on the right side of the valve as a reference it is easy to see which of the alternating sectors are in focus.

Fig. 6.

In Fig. 6 on the left is Biddulphia regina W. Smith. On top is the girdle view and below is the valve view. On the right is Actinoptychus senarius Ehrenberg, diameter 55µm, with the girdle view again showing the defining undulations. Actinoptychus is an interesting diatom found in the late Cretaceous through recent times with an explosion of diversity in the Miocene epoch.

Fig. 7.

This last image, Fig. 7, is two examples of Goniothecium odontella. As shown the width and height of the girdle can be quite varied. The diatom on the right was a little difficult to stand for imaging the valve, its top like shape guaranteed an oblique view. The width of the two valves are left 83µm and right 54µm.

The two diatoms in Fig. 1 are recent and the remaining diatoms Fig. 2 through Fig. 7 are fossil diatoms from the Miocene epoch. All the diatoms are from Newport Beach, California. The bar in the lower right corner is 10µm.

For instructions on sedimentation see 'sedimentation procedure' in Frithjof A.S. Sterrenburg's article 'CLEANING DIATOM SAMPLES'.

Comments to the author are welcomed.

References :
Round, F.E., Crawford, R.M., Mann, D.G., "The Diatoms. Biology and Morphology of the Genera", 1990, Cambridge University Press.
Schmidt, Adolf, "Atlas der Diatomaceenkunde", CD-ROM edition. [Editor's note: Available from Savona Books, UK.]
Van Heurck, Henri, 1885, "Synopsis des Diatomees de Belgique". http://sdrc.lib.uiowa.edu/algae/vanheurck.
Vinyard, William C., 1979, "Diatoms of North America".
Wornardt, Walter W., 1967, "Miocene and Pliocene Diatoms from California", Occasional Papers of the California Academy of Sciences, No. 63. San Francisco.

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