univited critters

[Northvan]

New to salt, have 2 new critters, one is some kind of nudibranch,want to know if its a problem in a reef tank, the other looks like a large centipede, maybe a bristleworm? I will try to attach pictures (new to this too). the nudibranch kind of looks like xenia (maybe thats what it eats?) the centipede thing is about 4 inches long & pale, came out after lights out. .....My pictures wont load because " a security token was missing" ....Can anybody tell me what I'm doing wrong?