They look just like little shrimp! Which reminds me of something really silly, a real "blast from the past"! Is anybody else here old enough to have read comic books as a kid, the ones that had all the neat stuff that you could send away for advertised on the inside covers? Things like smoke bombs, itching powder, and the x-ray glasses that let you "see through walls", and of course the ever-popular SEA MONKEYS! They were advertised as "instant pets" ... you just add water and they come alive! The ads showed these little creatures wearing clothes and doing human-like things like riding tiny bicycles. I
desperately wanted those when I was seven or eight - my mother always said, "No"! Turns out that what you really got for your 25 cents was
brine shrimp eggs! Apparently they are like tiny little shrimp ... and the eggs can be completely dried for long periods of time, then when water is added, they re-hydrate and continue to develop, hatching in to tiny little shrimp! So apparently what you have is some species that does the same thing! Have you checked on the bottom to see if there are any little hats and coats or little bitty bicycles?