I had the white flatworms years ago. They are attracted to light, so if you can rig up a light against the glass, they will all congregate there and you can use an airline tube to suck most of them out. I just waited them out and they enventually all just died out. If you want them gone sooner, you can use "flatworm exit" to get rid of them entirely.
A wrasse will probably control them too.
They look like juvenile stomatella snails to me
Notice that they all have the same "dark" blotch at the same place on each individual
I think that is the forming shell
Just my 2 cents