Oof kinda hard to see, if you could get a closeup pic that would be great, but look like red planaria which are a type of flatworm and not good, they aren't like harmful, but they do grow extremely fast and would smother corals if allowed to reproduce quickly. Just get a wrasse from haliocheres family such as melanarus, yellow coris, christmas, etc. and they will eat up all of them and keep your tank free of flatworms/bristleworms!