Iv'e had what looks like that on my shrimps a few times. Looks like Scutariella Japonica. I just dip them in a salt solution for about 30 seconds or so and the little buggers drop off. You need to keep en eye on them for a few days see if it comes back. I pull out any molts I find for a few days I think the eggs can stay with the molt and spread to others if they eat the shell. The salt dip has not affected my shrimp at all at least not that i can tell. I use 1 tablespoon opf aquarium salt per cup of water.
Gave them all a salt dip one by one a week ago. No sign of that stuff on them anymore. Have a new bit of confusion though. One of my shrimp seems to have some yellowish masses on it's inside. Not really sure what they are but it seems a bit sluggish today. Any idea?