What is this?
 

I guess I am being a little lazy - but I really don't have any idea. About 3 or 4 inches long and probably around 3/8" thick.

and ... for the bonus round ... is it bad/good for my tank?

http://www.canreef.com/vbulletin/pic...pictureid=6595

Thanks,

Jon

Bristle worm, harmless but gross.

Looks to me like a bristle worm and good for clean up crew

Very good cleanup crew, yep. Just make sure you avoid touching them with bare skin -- thousands of tiny thorny spines just ready to implant into your skin ;)

I hate the lil buggers but have learned to live with them and if you have one you will have dozens if not hundreds more also as Craigwmiller stated they are the porcupines of the ocean and if you happen to get some bristles impaled in you dip your affected body part in vinegar the vinegar will dissolve the bristles