Hi Frans - I would have assumed in this context - on the surface of water, in close proximity to the ocean, in August - that a floating gray springtail association were Anurida maritima. Any advice on how to recognize these as Hypogastrura and not Anurida? To my eye, Hypogastrura generally appears to have proportionately longer antennae than Anurida, but I'm not able to make that out in these photos.

The reason is indeed the context : a pool on a freshwater stream.
A. maritima is typically found on tidal pools at the coast. So not on freshwater but on seawater (salt water).
Hypogastrura specimens are often trapped on freshwater pools, and form a gathering of 100 or more specimens. They can only escape from the pool if they crawl on eachother and jump away from the pool. If they do not reach the edge of the pool, they will glide back to the springtail mass. BTW, I suspect that Einstein must have seen this behaviour of springtails on a watersurface and he must have got his idea of spacetime from that observation ;-)
The resolution of the shots is too low to use morphological characters, such as number of ocelli (5 in A. maritima, 8 in Hypogastrura) or chaetotaxy (distribution of setae on the body).
If the habitat description is doubthful, then we have to move the ID up in the taxonomic hierarchy : Poduromorpha.

Check out the video on YouTube for proof that these springtail were indeed in a fresh water spring pool.
https://youtu.be/IcGPwfUEH-A

gives an error msg : Not available. Private.
:-(

It should be viewable now

Still the same problem. I did a search at youtube and could not find any clip on Collembola with title 'The Writhing Masses'... I could find other interesting clips with that title, though ;-)

https://www.youtube.com/watch?v=IcGPwfUEH-A

I was attracted to these guys by their constant movement and got to wondering how such fanatical movers could all wind up in the same place. Kinda like how static electricity attracts feathers, perhaps feathers (and/or dead spiders) attract these guys.
But as interesting as they were, I got distracted by the other beauties of the Maine coastline in August, and moved on to other subjects.
However, I'm now regretting that I didn't grab a few out of the water and made a couple of macro captures.
Maybe next time!
Though as I get older, "next times" are fewer and farther between.

Yes it did work now. Thx for fixing.
It is also clear now that this is not Hypogastrura sp. The behaviour on the watersurface is atypical for Hypogastrura. I did not see 1 specimen jumping. All specimens were only crawling about. Anurida maritima does not have a furcula. It can jump, though, using a special technique. But I did not see it being used.
The conclusion : it is not Hypogastrura but Anurida maritima, as Joshua suggested.