Nudibranch?

I'm new to the SW scene and got 75% of my LR from an established tank and the other 25% from a store. I have found an interesting amount of hitchhikers so far. I think I find a new one everytime the lights go out in the tank. Yesterday it was a 5" bristleworm (5" exposed at least) and tonight I saw what appeared to be a slug. I googled it and the only "slugs" in SW tanks are nudibranch. I hope someone can ID this guy from my horrible picture and let me know if he needs to be removed.

Tank currently has reef hermits, turbo snails, peppermint shrimp, true percula clown, zoanithids, and an open brain. Please let me know if any of these are at risk.

Thank you

Thanks for the quick response. I love the experience/intelligence on this site. You guys could ID anything even in the worst pictures. lol. I like to know the names of eveything in my tank but most importantly if they pose any harm to anything else. I thought snails had shells and slugs did not. Shows what I know. He sure was a quick mover for having no legs.
Also, the only reason I found him is because I noticed one of my reef hermits was dismembered and I did surveilence on the area of his remains and this guy popped out. He doesn't look like much of a fighter though so I guess he was in the wrong place at the wrong time and was framed.

Amphiprion said:

It has a shell . It is actually very flattened (and uncharacteristic of Trochids), but it's there. Touch it and you'll see what I mean.

Click to expand...

No thank you! I used to finger all my rock not knowing what inhabitants it had/could have.

While we're on the subject of hitchhikers, I hope you do not mind if I hijack my own thread. Granted not all of these are "marine inverts" persay and may not belong in this forum, but you can flame me later.

1.)Sponge...thingy?

2.)Calcerous tubing like a feather duster, yet the thing protruding is white and fleshy. Nothing feathery about it. Just a chunk of white... mushy stuff. No idea here. Sorry for the bad picture and even worse description.

3.)Bristleworm and harmless?

4.)Got this zoo frag and thought this shell was just part of the rock. Upon closer examination it seems to have small hairs coming from the (mantle?) and seems to open/close at times. Zoos will not grow over it. Sorry again for the bad picture. Aquariums are not easy things to photograph at close detail. Would have to pull that frag out and get a top down picture or something.