If this was back east, they would have been tadpoles, but they were rather too small and speedy for that. I took a little bit of water home with me in a cup to look at under a magnifying glass, and it confirmed what I guessed; freshwater copepods.
But now the little world is dried up. But the creatures that depend on such vernal ponds are adapted to that. I'm sure that encysted in the mud, another generation of algae and copepod are waiting for the next season of rains. Or travelling to other waters on the legs of birds or the wind.
And a few are now living in my small aquarium, which is otherwise the home to snails and anacharis. I haven't decided if I'll introduce them to my six-gallon, but they seem a perfect fit. Plenty of algae for them to eat, and danios to eat them.