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How to study gastrotrichs

Posted: Thu Aug 01, 2019 4:23 am
by gastrotrichman
A wealth of introductory information on how to study gastrotrichs was published last week. The paper deals with both marine and freshwater gastrotrichs and includes keys to families and genera. Professor M. Antonio Todaro is the senior author and is a world expert on gastrotrichs. An open access copy is available at:

Re: How to study gastrotrichs

Posted: Thu Aug 01, 2019 7:42 am
by MichaelG.
Not really my area of interest, but I have to say:
That looks a superb piece of work ... very nicely structured.


Re: How to study gastrotrichs

Posted: Thu Aug 01, 2019 3:37 pm
by Sauerkraut
Thank you. Very nice drawings with detailed labeling. I've bookmarked this.

Do you slow these guys down for viewing with methyl cellulose too or something else?

Re: How to study gastrotrichs

Posted: Fri Aug 02, 2019 1:20 am
by gastrotrichman
Sauerkraut --

Yes, gastrotrichs tend to be very active and have to be slowed in order to see characters needed for identification.

A 1 percent solution of magnesium chloride is often used for freshwater species, and a 7% solution for marine species. Magnesium chloride is hygroscopic and can vary from anhydrous to hexahydrate, which complicates specifying or achieving consistent concentrations. I usually use a roughly 0.5 percent solution with good results with most freshwater species. I find that magnesium chloride eventually kills gastrotrichs, whereupon decomposition sets in … although many features can still be seen for a while, internal features tend to become obscured fairly quickly.

With patience, gastrotrichs can be slowed and eventually stopped by allowing evaporation of water from under the coverslip. A specimen can be maintained partially compressed for hours by judicious addition of water from time to time to prevent the coverslip from crushing it.

Most students of gastrotrichs support coverslips to avoid crushing specimens, especially the larger ones. Broken pieces of coverslips, modeling clay dots, and fine beads of petroleum jelly along two, three, or four sides of the coverslip are among the things used to support coverslips. I prefer beads of petroleum jelly because they allow fairly delicate adjustment of compression.

Re: How to study gastrotrichs

Posted: Fri Aug 02, 2019 11:22 am
by 75RR
I prefer beads of petroleum jelly
Had not heard of these. Can you provide a link please

Re: How to study gastrotrichs

Posted: Fri Aug 02, 2019 3:23 pm
by Sauerkraut
Thank you for the detailed info, Gastrotrichman.

Re: How to study gastrotrichs

Posted: Sat Aug 03, 2019 12:25 am
by gastrotrichman

Sorry, I don't know of a link. I learned the technique from a longtime gastrotrich student in New Jersey.

I apologize for using the term "beads" of petroleum jelly without explanation. I was thinking of "bead" in the sense of a bead laid down by a caulking gun.

Smear a little petroleum jelly into a thin layer on a smooth surface. Hold a clean coverslip by its edges between thumb and forefinger, lower the opposite edge into the layer of petroleum jelly, and drag the coverslip a millimeter or so at a 45-degree angle to pick up a small "bead" of petroleum jelly. Reverse the coverslip and repeat so that opposite edges bear beads. Add a bead to a third edge if you wish. Lay the coverslip on a flat surface bead-side up. Place a small drop of water or magnesium chloride solution (1% for freshwater species; 7% for marine species) in the center of the coverslip. Transfer a gastrotrich to the drop using an Irwin loop or a fine pipette. Place the coverslip on a clean slide with the beads and droplet side down. Adjust compression by carefully pressing down on edges of the coverslip while observing the gastrotrich under low magnification.

Gastrotrichs are easily squashed, so use care in increasing compression. Magnesium chloride will soon kill freshwater species, which leads to decomposition, particularly of internal features (I don't know about marine species). Gastrotrichs will live for a long time in water without magnesium chloride, and can be kept alive for hours if water lost to evaporation is carefully replaced periodically. I prefer small drops of water to keep gastrotrichs from getting lost where larger drops make contact with the petroleum jelly. Magnesium chloride has a number of hydrates, which complicates calculating aqueous concentrations; adjust the concentration down if it kills too quickly, and up if it doesn't immobilize within a few minutes.

I hope that helps.

Re: How to study gastrotrichs

Posted: Sat Aug 03, 2019 2:12 am
by tgss
Petroleum jelly can also be dispensed from a syringe (the syringes used for dispensing small quantities of glue for example). A small bead, that is a spherical bead, can be squeezed onto each of the corners of a coverslip, which can then be treated as described by gastrotrichman. I got this idea from Wim van Egmond in his lecture to the Quekett club on "The Mysterious Soil Life Video Project" A video of the talk is available on the Quekett web site (may be available to members only - I'm not sure), and about 4' 50" into the video the process is pictured.

Re: How to study gastrotrichs

Posted: Sat Aug 03, 2019 4:26 am
by 75RR
Many thanks to both gastrotrichman and tgss for the clarification.

I admit I was thinking of squishable mini beads (as in little round ball filled with vaseline) :)

I had heard of but not yet used vaseline to seal the edges against evaporation. Had not thought to use it to fine-tune the cover slip height.