hey guys i have a few questions on flatworms but first let me add some background information, i currently have a nano aquarium set up for a G. chiragra mantis shrimp and i has some other cuc in there as well but no corals or fish just a marine planted tank if you will dominated by macro algae. When i added the last round of macro to my tank i accidentally introduced what i believe to be flatworms. They are small only reaching about a 16th to an 8th of an inch in length total too small to really get a clear picture with my phone, and when small they are a light cream to tan and as they grow they take on the bright green coloration of the feather caulerpa in the tank. I have been keeping there numbers down by manually removing them during water changes, but haven't tried anything else. So my questions are as follows... 1) Are these little critters indeed flatworms? 2) If so do they pose a threat to anything in my tank such as my mantis shrimp(I've heard some eat corals but again i have no coral i just haven't heard if they can harm anything else) 3) Should i remove them all together? 4) If so what is the most effective manner in which to do so that is safe for my mantis shrimp?