Please help with identification of a very small circular organism

[mazo4033]

I found this very, very small circular organism and have no idea what it is. I've looked at all the identification guides I have, but was not able to identify the organism. The images and videos attached below are at 400x magnification. This organism is very smooth and has a circular shape, however, it can change its shape to a more pointed oval-like shape. It was found in a sample from a pond (or lake?) that has no algae on the surface. It is a completely clear body of water. I think there may be fish in the water because I believe fly fishing is allowed at this place, which indicates the presence of fish. This organism is incredibly small. I don't know the exact size in micrometers, but it was invisible under 40x, visible as a small dot that I barely noticed under 100x, and still pretty small in these pictures under 400x. Upon examination, this organism did not seem to have any flagella. I checked under an oblique illumiation filter that I made and still did not see any flagella. It moves very fast, though, so maybe it does have cilia (or perhaps flagella?) that were not visible. The organism is completely clear and colorless, with the exception of the inner, smaller circle that has a hint of green. Something interesting about this organism is that it does not seem to have any organelles. There is just that one green circle inside. The organism does seem to have layers, though, as it has an outer circular line, but then another circular outline inside, and then inside that the green circle. So it does have a cell membrane. This organism is also three-dimensional, as one of the positions I found it in was sideways, in a lateral view. It seemed to have an orb-like shape, where there was a line down the middle and its sides protruded outwards. I found this organism in three positions: circular and flat, "pointed oval shaped", and sideways orb-shaped. However, the organism is very fluid in its shape and had some other "half-way between a circle and an oval" shapes. It moves very fast, in a circular pattern, as well as twisting as it moves straight. There is a video I attached below of its movement. When moving, it shapes itself from a circle into the "pointed oval shape". I only found one of this organism in the sample. Truly fascinating. I don't think it is a protist. Any help in identifying or more information about this organism is greatly appreciated! Thank you!

Here are photos and a video.

This is the circle shape



This is the pointed oval shape



This is the orb shape



This is one of the other shapes



This is under oblique illumination



Here is the video of its movement
https://youtu.be/oO4sCgXRCYo (I don't know why it is not showing as a video and just a link, but just click on the link to see the video)

Thank you!

[Charles]

Picture and video isn't quite clear, but I would say it moves like a Phacus.

[mazo4033]

Thank you, Charles, for mentioning Phacus - it does move a lot like Phacus does! But it doesn't look like Phacus which is what still makes this organism a mystery.

[ProtistAdmirer]

That’s strange. I’d like to know what it is too. The Facebook group “Amateur Microscopy” has some experts who may be able to identify it if you post it there.

[mazo4033]

The Facebook group “Amateur Microscopy” has some experts who may be able to identify it if you post it there.

Thank you for letting me know, ProtistAdmirer! I'll check it out.

Maybe this organism is a small algae?

[mazo4033]

I have accidentally found what I think is the identification for this organism: Phacotus lenticularis!

[linuxusr]

My guess: If there is green, that is chlorophyll; if there is chlorophyll, it's in a walled body called a chloroplast; and a chloroplast is an organelle.