They are detrius worms. They are a about 1/4" at most. Hair thin, and white/clear. They are free-floating and sometimes they are seen on the glass.
They are common in tanks with excess organic matter, and tend to live in pre-filter sponge material or in your filter. They thrive in low current enviorments.
If this sounds familiar, then you shrimp/fish are safe. fish eat em, and they are NOT parasitic. Concentrate on cleaning your filter frequently and water changes.
I have some in my CRS/RCS/Amano tank. They also seem to show up when snails are present.