There seems to be relatively little documentation on BugGuide of this species, and (shockingly!!) mine seem to be the first observations posted from the entire western half of the US. As I have ample opportunity to observe and photograph them in my pond, I'd love to add more to the knowledge base. You mentioned that one of my other observations failed to showcase characteristic features for this species. Aside from the long, curved furca (which can be easily seen in the shed exuviae), can you enlighten me as to what other field marks I should aim to capture in subsequent photos?

shows a typical character : short abdomen. Note the abdomen is about equal in length as the thorax.
Other features are :
1. terminally rounded abdomen, never pointed
2. the unguis is very long : as long as the tibiotarsus
3. the eyepatch is quite particular. I call it 'twinkling eyes' : 4 ocelli form a square and inbetween those ocelli are raised ribs forming a cross.
4. in juvenile specimens, the legs and antennae are reddish while the body is blue
5. in very juvenile specimens the body and legs and antennae are all reddish
6. the spermatophore is deposited on the water surface and the stalk is very short

Thank you so much, Frans. Your list gives me lots to work with in my future photographic efforts. I will need to try and capture this better, but I'm curious whether this observation effectively shows the long unguis you mentioned:

it does. The elongation of the unguis is typical in species that live on the water surface. The unguis can become extremely long in cave species that live on the water surface of pools in the cave.
See for examples this Onychiuridae species :
https://www.collembola.org/images/thibaud/1986/Ongulonychiurus-colpus-1986-Thibaud-J-M-Massoud-Z-Spain-Fig1.jpg

Your link made me want to see an actual photo of O. colpus, but I couldn't readily discover one online. But, I did find this impressive image of another cave-dweller within the same family, Troglaphorura gladiator:
https://www.researchgate.net/figure/FIGURES-1-2-Troglaphorura-gladiator-sp-nov-habitus-of-alcohol-specimens-1-lateral_fig1_333866541

Wow!