Really cool! I'll say, it initially looks like a tardigrade. There are different species as well as classes of tardigrade. Some, depending on their environment, can look a little different. I think the typical idea of a tardigrade are tardigrades from the Eutardigrada class, but tardigrades from other classes (mesotardigrada or heterotardigrada) can look a lot different and more similar to your picture. Look at this for instance
https://www.researchgate.net/figure/Hab ... _318469778
If this is a tardigrade, my best guess is that it would be from the heterotardigrada class. But I feel hesitant to say that it is for sure a tardigrade or give a species. Here is why:
First, tardigrades tend to have 8 legs. Three on each side and then two at the bottom. But the two legs at the bottom typically look like the other six legs, or at least this is what I could conclude from images that I saw. In the case of this organism, the bottom appendages look vastly different from the first six appendages.
Second, tardigrades usually have 4-6 claws on each foot. The organism you found seems to have 5 or 6? It is hard to tell but there could even be more - there seems to be a lot smaller, wispy claws or appendages as well. But the legs in the front (near the head) seem to have only 3 claws? This inconsistency, as well as the fact that each of the other legs could have more than 6 claws (because of all the wispy, smaller ones) is really odd. But everything else looks like a tardigrade, which is what confuses me!
I decided to go the route of trying to identify this organism via the morphology of its claws. The link that I linked above has good pictures of claws with the species or family of tardigrade underneath. I unfortunately couldn't find a match to the claws of the organism you found. Nothing was as wispy and long as the claws of this organism. Most claws that I could see, and most species that I could find all had very short and curved, literally bear claw-like claws. The majority had four claws, too. But this organism has claws -- should I even call them claws? I'm not sure -- that look like a brush or a duster, something like that!
I found some that had similar claws, but nothing that was a match.
These are:
Stygarctus
Echiniscoides
Isoechiniscoides
Trogolarctus
But the claws are not a perfect match and if you search up those tardigrades, they do not look like your organism. Echiniscoides, which has the closest claw that I could find to the organism you found, has claws that are all sized nearly equally, that are thick, short, and curved. So not the claws (?) that this organism in question has. Moreover, nothing that I could find have the same head appendages as the organism you found does.
Lastly, you said that this organism moved quickly everywhere, but don't tardigrades move slow?
I looked at a bunch of pictures as well as some research papers. Unfortunately I couldn't find anything in terms of tardigrade that looked like your organism. I initially thought that this organism is a tardigrade, but after a little searching I actually doubt that it is a tardigrade.
Where did you find this organism? What kind of body of water?
In summary, I would say that the closest thing in terms of tardigrade to your organism is Echiniscoides from the class heterotardigrada. But I am not convinced that your organism is a tardigrade, even though it looks a lot like one. I'm not an expert at all, so maybe someone else will know more, and perhaps will have an ID!
These are just my conclusions from some googling and looking at papers and images. Hopefully it helps a little bit towards the identification of this organism!
