The floating coverslip

[tlansing]

Many of you on this forum will be very familiar with the floating coverslip technique. I am a very enthusiastic user of this technique and recently had some very nice results that I wanted to share on the forum. In a nutshell (a fuller explanation can be found on the excellent website of Martin Kreutz: https://realmicrolife.com/the-floating-coverslip-2/), a petri dish of pond water containing organic material (leaves, algae, parts of aquatic plants) is set up and one or more coverslips is/are suspended on the surface of the water (I simple drop 25x25mm coverslips flat onto the surface of the water). The surface tension of the water will prevent the coverslip from sinking. The coverslip is then allowed to sit for a few days to weeks while protists and algae in the water begin to colonize the underside of the coverslip. The coverslip can be periodically removed from the petri dish using a stamp collectors forceps and examined under the microscope. The coverslip can be colonized rather quickly, often in a day or so, and the diversity of organisms on the coverslip changes over time. This method also is fantastic for photography, as the organisms are attached to the underside of the coverslip and are often nicely flattened to the underside. I often observe a wide variety of sessile and motile organisms and some of them can be more easily observed using this method than a normal wet mount, such as some small testate amoebae. Here are some photos of my recent findings. The microscope is a Zeiss Photomicroscope III with a Canon 1300D camera attached.
The rotifer Collotheca. 16x plan acromat, 1.25x optovar, DIC with flash

Collotheca.jpg (79.51 KiB) Viewed 829 times

The flagellate Cryptomonas. Note the extrusomes (the rows of dots). 40x Neofluar, 2x optovar, DIC with flash

Cryptomonas.jpg (42.58 KiB) Viewed 829 times

The vampyrellid amoeba Hyalodiscus. These are fascinating to watch move by a “rolling” forward motion. They are not too fond of the light! 40x Neofluar, 1.25x optovar, DIC with flash

Hyalodiscus.jpg (94.19 KiB) Viewed 829 times

The desmid Micrasterias radiosa. 16x plan achromat, 1.25x optovar, DIC with flash

Micrasterias radiosa.jpg (121.04 KiB) Viewed 829 times

The testate amoeba Pyxidicula. This is a very tiny testate amoeba that I have seen very often on my coverslips. The opening in the test (the pseudostome) is almost as large as the test itself. I have never seen pseudopods emerge from the test. Note the round nucleus and a contractile valuoe next to it. 100x oil immersion, 2x optovar, DIC with flash

Pyxidicula.jpg (51.53 KiB) Viewed 829 times

[tlansing]

Here are a couple of additional photos. These are the colonial flagellate Rhipidodendron. The large colonies are difficult to photograph in wet mounts but they can grow to large size on a coverslip. I had been hoping to find one like this. The first photo is 10x F achromat, 1.25x optovar, phase contrast to show the size of the colony and more detail can be seen in the second photo, 16x plan achromat, 1.25x optovar, DIC with flash.

Rhipidodendron-phase.jpg (147.33 KiB) Viewed 827 times

Rhipidodendron-DIC.jpg (100.47 KiB) Viewed 827 times

[macnmotion]

All wonderful, but I'm a sucker for Collotheca. A fantastic look at it.

[SuiGenerisBrewing]

That is an amazing technique. Reminds me of the "hanging drop" method we use in the lab to reduce the amount of antibody (which is stupidly expensive) we use to immunolable samples. A small amount of the antibody solution is placed on a hydrophobic surface, and the sample on a coverslip "floated" on top of the drop. I never though to use it to colonize a coverglass - I need to give that a try,

I also wonder if this wouldn't be a good way to make permanent (or semi-permenant at least) mounts of pond water organisms; presumable the coverslips could be fixed and mounted in a mounting medium once sufficiently colonized.

[tlansing]

@macnmotion: Glad you liked the pictures, thanks. I also am always excited to see the spectacular rotifer Collotheca. It is really cool to see them contract and then extend their setae. It is also cool to see them "gulp" their prey.

@SuiGenerisBrewing: The floating coverslip is really a great technique and so easy to do. As far as preparing permanent mounts from them, I would think you would have to be able to affix the organisms more firmly to the coverslip. Long ago, I remember affixing ciliates to a coverslip using Mayer's albumin prior to protargol staining, so something like that might work.