Worm?

[bignose]

It's in your refugium I don't think you should have any problems with it.

[Nano]

the best way to tell is a picture even if its a crappy one, it helps a lot more to see the body shape, size, etc. have a look on http://www.chucksaddiction.com/hitchhikers.html
you might be able to find him on there

[pat18]

Thanks for the replies, i went on the link and to me it looks most similar to the Eurythoe complanata, but it was small so it is a little hard to tell