I came across one of these quite awhile ago, but my camera was unavailable. I found several of these on my slide, but this one seems to be the best representation of all of them. Taken outside the coverslip, couldn't find any under the CS. They get long, perpeptually seem to be dividing, yet they never seem to complete the division process. VERY thick, rich and abundant celia. Don't move much. Huge vacoules.
20X Brightfield
20X Oblique
20X 'Darkfield' (sort of. This is produced by changing my oblique filter)
Very odd. My first thought was that it looks like one of the Astomatea / Astomatida (Haptophryidae, Radiophryidae etc.) Many of them produce catenoid colonies...kind of like half-finished transverse divisions that hang on behind the mother cell (proter), and some have anterior holdfasts that resemble the front of your creature. However, they are parasites (endosymbionts, really) of larger animals, such annelids, flatworms, molluscs and amphibians. They should not be found swimming free. Some Thigmotrichs form catenoids, too, and are very "hairy"....but they're also parasitic.
So...I have no idea. I hope somebody else knows these guys.
I made my scale using Corel Draw.
Photographed my digital micrometer at 50um
Had to scale for the higher power objectives.
It's not as accurate as many, but I suspect it is good
enough for basic photography.
I haven't found anything eiter. I checked out your leads, Bruce, and they do look similar. Still...the only thing big enough in my 'pond' for these are some crustations (they look like shrimp), and some red worms. They are worms, too, not larva. There used to be flatworms, but I haven't seen any now for months.