Good thing or bad thing?

[caymanada]

My tank is two weeks old and this thing crawled out of the rock last night. It never fully came out of the rock, but about 2 inches of it was showing. I think this is some type of bristle worm (?). Do all bristle worms have the ability to sting? I have read some mixed reviews, should I keep it? Should I try to get rid of it?

[bluwtr]

Yeah it's a bristle worm and they are fine. Great detritovours.

[caymanada]

Update: I have 2 of them. They are each about 3 to 4 inches long. Does anyone know if they are the stinging type? Thanks.

[AgeDynasty]

Be aware, they could be fireworms, which are bad. Sounds like fireworms being that there that big.

[Amphiprion]

Well, the one in the pic doesn't look like Hermodice carunculata, which is the true "fireworm." That species has a bright red, highly visible tuft on the head, known as the caruncle (hence the scientific name). While all amphinomid worms are actually otherwise known as fireworms, only the big predatory ones are called that in the hobby. Hobbyists call all the other amphinomids "bristleworms" in general (even though that term applies to all polychaetes, which includes things like featherdusters).

Anyway, I suspect your worm is Eurythoe or something very similar. These worms can get quite large--on the scale of Hermodice--but don't have the same predatory habits and most stay smaller. They are, ounce for ounce, one of the best carrion eaters and, as bluwtr mentioned, are great detritivores. While there are bad worms, most are good thing . Besides, that is mostly what you pay for when you get live rock or harvested live sand.