I'm thinking these are like purple flatworms. There are a few around but they mostly hold up in hairy mushrooms and you can barely see them because of their color. However I have spotted some on corals like this Lobo and Duncan. They have been around for some time, (month or 2 maybe more) but I really haven't noticed any damaging effects from them. The questions I have are: What is it, and should I treat/remove them? any advice would be appreciated. Thanks!