With Some Attention to Gastrotrichs
Richard L. Howey, Wyoming, USA
Jack and Jill went up the hill to collect a pail of water. As various disorders creep up on me and make it harder and harder to get out to my favorite collecting spots, I find that I have to try to con some hapless student into going along with me and doing most of the work. However, I have found a means of supplementing my few expeditions into the wild.
One summer, I happened to leave a 5-gallon plastic bucket sitting below a hanging planter of lovely lobelia out on our patio. When I watered each morning, the excess would drip down into the bucket. That part of the patio gets a good deal of intense sun and after a couple of weeks, I noticed that I was getting a healthy grow of algae–a lovely green scum. I began to keep an eye on the bucket to make sure that there weren’t any “wrigglers” in it; I didn’t want to be responsible for contributing to any growth in the mosquito population. However, I didn’t want to simply discard what might prove to be an interesting source of microscopic critters.
Summers are both busy and lazy and so it was several weeks before I got around to taking a sample from the bucket to my lab for examination. Well, there were certainly lots of filamentous algae and as I looked around, I noticed some wrinkled blobs on the bottom of the dish–Thecamoebae!
I had seen a few specimens on a previous occasion, but in this sample they were abundant and feeding enthusiastically on the filaments of algae. Here is an article which I did on Thecamoebae and one image shows one having a snack.
For this image, I had stained some of the filaments in the culture with a dilute solution of Neutral Red and you can see that some have been ingested.
This year when the summer was only half over I had 4 containers which I finally sampled and found the “inch worm” rotifer Philodina in great abundance, Vorticella, Colpoda, Paramecium, nematodes, enormous numbers of euglenoids, an abundance of colorless flagellates, several type of filamentous algae, Arcella, quite a few large hypotrichs, gastrotrichs, and a considerable variety of small non-filamentous algae as well as the ciliate Litonotus, and a number of specimens of Amoeba “radiosa”. The reason for the quotation marks here is that “radiosa” is probably not a legitimate species. A number of investigators have suggested that a variety of species of small amoebae, especially soil amoebae, take on a form with a more or less globose center from which radiate a number of pseudopodia that taper to a “sharp” point. This condition seems to be most prevalent when they are not attached to a substrate.
This is probably a specimen of Mayorella, but I’m not an expert on amoebae and the small ones are a taxonomist’s nightmare. Clearly with many of the very small protists, techniques beyond optical microscopy have been employed which are beyond the scope and means of all but a very few amateurs.
The populations seems to vary according to a number of factors. One bucket sitting at the back of the driveway had some yard trimmings in it and received only rain water. Two containers without any vegetation in them which had been sitting inside our very old garage–it was built in the 1890s and the roof leaked–had water filtered through the wooden shake shingles and one had some soil which washed over into it from the plants hanging above it and had a mix of rain and chlorinated tap water. So, we have some variations in the solid material ranging from one with no vegetation to a mix of soil and vegetation; variations in water; variations in soil. Some of the patio plants were shipped from nurseries in the southern part of the U.S. and when I potted them, I used 2 or 3 different brands of potting soil and heaven knows where they came from. Perhaps the fact that fascinates me most is the chlorinated tap water. The reports which we get from the city of Laramie regarding water quality tests indicate that it is first-rate. Sometimes, in our small bathroom, which has 2 basic functions: 1) to allow me to maintain the second basic virtue–cleanliness, since I make no claims to being godly and 2) it serves as a place to wash the glassware from my lab. The reason I mention this is that sometimes I have to let the water run a bit to get any warm, let alone, hot water and in that very small space there is at times the distinct odor of chlorine. Nonetheless, my bucket beasties not only survive the chlorinated water, but seem to thrive in it.
Chlorine bleach is widely used in hospitals, universities, and research institutions to kill bacteria and viruses and while the levels of chlorine in drinking water are quite low, it is, nonetheless, a tad disconcerting to find a wide range of organisms that can tolerate even tiny concentrations.
I mentioned gastrotrichs a bit earlier. These organisms, like ostracods are often overlooked because the are quite small, move rapidly, are difficult to study, and often are not easy to classify. At one time, I was quite annoyed with gastrotrichs. That was when I was trying to find a protocol for culturing Lacrymaria olor and gastrotrichs of the genus Chaetonotus kept appearing in abundance in my cultures. I observed a number of encounters between these two organisms which were intriguing because when there was actual physical contact, both seem to quickly withdraw as though each had been stung, although neither seemed to suffer any permanent damage.
Relatively little systematic work has been done on gastrotrichs, especially the freshwater species and so rather little is known regarding their geographic distribution. What this means for the amateur is rather exciting, for serious and careful investigations of a particular region are fairly likely to turn up new species and, if you find and describe one and get it named after you, there may be a bit of immortality lurking in the wings.
If I were doing an F.B.I. report on gastrotrichs (a Freshwater Biological Identification report), it would look something like this.
Size: 70 to 600 microns; average 125 to 325
Shape: tubular; anterior end rounded, sometimes lobed; posterior has 2 toe-like projections with considerable variation in length. Each has a cement gland for temporarily attaching it to a substrate.
Surface Structures: The body is enclosed in an envelope of cuticle which is usually patterned with overlapping scales and may have some small ridges or spines and these latter can be short or very long and are taxonomically useful.
Sensors: One or two pairs of colored eyespots occur on the sides of the brain, but their purpose is uncertain.
Muscles: There are several pairs of muscle bands that run virtually the entire length of the organism. When these contract, they produce some striking gymnastic contortions.
Movement: These creatures slide along the substrate with rather elegant gliding movements produced by their carpet of ventral cilia. There are some species with long spines that seem to give them an ability to appear to be jumping through the water.
Nervous System: For its size, this creatures has a rather large brain and two long nerve strands. The brain is located over the upper portion of the pharynx.++
Eggs: Almost all marine gastrotrichs are hermaphroditic; all freshwater species are female and reproduction is parthenogenic; no males are known, so take that all you male chauvinists! Two distinct kinds of eggs are produced, one which, as soon as it leaves the body of its parent, begins to develop; the other is produced when conditions become adverse and these can survive heat, freezing, and drying for a period of several years. A biologically shrewd creature, survival-wise.
So, there’s the profile and they can easily be identified by screeners at any major airport. If you want to culture them, you might try adding a bit of malted milk powder to your culture dish. That’s what I was using when trying to culture Lacrymaria and, on the side, getting abundant populations of gastrotrichs. They can be fixed in a 10% solution of formalin and stored in 5% formalin or 70% alcohol. Some species reject such harsh treatment and become severely distorted and so must be anesthetized. Again one has to rely on trial and error. Sometimes one can get good results by using menthol, but if that’s not successful, it’s worth trying a dilute solution of ethyl alcohol (vodka), magnesium sulfate, or, if you have access, chlorotone or hydroyxlamine hydrochloride. Once these have taken effect, they must be followed by a fixative.
My bucket cultures have provided many hours of observation of interesting organisms and there is significant variation from year to year. For example, this year I found no Thecamoebae whereas previously, they were abundant. In previous years, I didn’t find gastrotrichs, but these strange little creatures are certainly worth spending some time investigating.
All comments to the author Richard Howey are welcomed.
Editor's note: Visit Richard Howey's new website at http://rhowey.googlepages.com/home where he plans to share aspects of his wide interests.
Published in the November 2019 edition of Micscape Magazine.
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