ID this worm plz ?

[Gregs]

hey everyone, been fresh keeping all my life and now im switching to the darkside (for my wallet) - setting up a 220g fowlr and everything is ready to go. i got a load of live rock but as I was moving them from bucket to bucket one of these guys fell out... and then another... and another... all in various sizes.
bad?
good?
if bad, how would i erradicate the critters before throwing the rock in the tank?

thanks,
cheers