White and brown millipede worms??

[LacroixBoy]

Hey folks, just noticed these small worm/millipede like things in my tank. I think they come out at night and they are really fast. They dart back into the rockwork before I can get a good look usually. I have no idea what these are and I’ve dipped every coral I put in. I’m pretty upset that they managed to get in. I’ve seen a handful now and theres a bigger and longer one I haven’t gotten a look at yet but its peeked its head out.

Anyone know what these are? They don’t look like bristle worms I’ve seen.

 

[Crabs McJones]

amphipods

 

[LacroixBoy]

The big one seemed long like a worm, does that still fit? And if so are they bad?