please can some one give me some advice on how to get rid of a fire worm from my marine tank. it has eaten my fire shrimp and some of my hermit crabs. i am worried about my fish as this thing is starting to eat through my tank
They do make bristleworm traps. The problem there is if you have a bunch of bristleworms, you may catch them instead of the fireworm.
The bigger questions, are you sure you have a fireworm? And, are you sure it killed the shrimp and hermits?
Bristleworms are basically kept in tanks for clean-up duty. If a fish/invert dies the worms are very good at disposing of the body. This often leads to them being blamed for the death, when in fact they are doing exactly what the aquarium owner put them in the tank to do.
I would have to agree with Khemul. In the vast majority of circumstances, the worms in our tanks fulfill an important purpose--everything from eating carrion and detritus to actually eating algae (who doesn't want free algae eating animals?). They aren't the prettiest things, but they are quite useful in most cases.
In your particular case, if you could provide some images of the worm in question, it would be very helpful. If you have a true "fireworm," then they have a preference for coral flesh. You would see them munching on an unsuspecting coral at some point. They greedily eat other things, but if you have corals, then you'll know for sure. I'll also second the question posed as to whether or not you actually saw the worm feeding on your shrimp and crabs? The fireworm, Hermodice carunculata will indeed eat these things, though.