100% positive this is planaria. not really harmful (some fish actually will eat them) but they indicate poor substrate maintanance. do some nce gravel vacs with your water changes and they should disappear.
nothing to be overly worried about.
cheers
No they are not harmful - they are planaria. they won't hurt the fish, but they are a symptom of too much gravel containing too much uneaten food, and that is not good for fish. They require a food source, which means there must be excess food wastes in the tank to support them.
Give your gravel a good deep vac and cut down on the feeding.
Its very strange as its only had the gravel in for about a month now as its a new setup. Had it running for alot longer without gravel in. I only put one tablet in a week which all gets eaten fairly quick by the shrimp so i would not know why the gravel would have excess food in.