Without better photots, I am going to say planaria or some kind of detritus worm.
Are you suplemental feeding? How often? have you ever done a good deep gravel vac?
If your shrimp are not dying and you do not see them being attacked by these worms, then its really only your preference on letting them stay or not. If you are feeding, stop. Do a deep gravel vac, stir that gunk up, and WC the bulk out. Increase the volume and frequency of your WCs...50% every other day isn't going to hurt your shrimp.
If that doesn't work, look at fenben....OTC dog dewormer. Small doses are usually death for the worms and not harmful to shrimp or snails.