I would think its planaria. They look like mini flies to me and they dash around very fast. I'd say the size of a period - . The baby shrimp I have are around " _ or __" long. Very small and clear.
just noticed these things arent white. they look white when on the glass i guess they have white bellies but are darker on top. yes thats about the correct size of these things. im used to the opaque flat planaria and larger. yes the baby shrimp i've seen are these __ size havent seen any smaller.
im thinking about adding a small whitecloud in my shrimp tank to see if they can eat them. any other suggestion for fish in a shrimp tank that may eat these things or hydra (those are in my other tank and i've noticed tiny bugs on the surface).