The Arrow Crab, also known as the Spider Crab, has extremely long legs. It is called the Arrow Crab because of the shape of the body and head. The size is variable, many reaching six inches, and some up to 10 inches. Females may be dramatically smaller. Different species inhabit different parts of the world. The most common Arrow Crab (Stenorhynchus seticornis) comes from the Caribbean, but other species are imported from the Indo-Pacific region, eastern Africa, and California. They normally inhabit portions of the reef usually associated with a small cave or crevice. It is a hardy, long-lived invertebrate, that can be housed in the reef aquarium. This crab has been known to attack crustaceans such as Banded Coral Shrimp, and may even attack small slow moving fish. All crabs are opportunistic feeders and if insufficient food is present they may pick at mushrooms or polyps searching for food. Breeding Arrow Crabs in the aquarium is not generally successful. Larvae are free-swimming and hatch in about two weeks. It will accept almost all meaty, flake and tablet foods.
They are bristle worms..and brittle stars..that you are asking about...
I've yet to see a bristle worm (even the larger ones, and I've had some huge ones.. 12 + inches long) damage a coral or harm an invert. They are detritus eaters and mostly keep to themselves in the rock work although they will come out and forage for food if there is anything laying around on the sandbed at night (food wise).
The smaller bristle worms also are detritus eaters and also cause no harm to the tank.
Bristle worms wil only grow to large populations if you overfeed your tank as they are a self limiting population based upon the availability of food. You cut back on feeding too much and they will die off to a more acceptable level.
Mini brittle star (fish) - the ones you see in the 1/2" - 1" range are also great for your tank and eat detritus. Good guys
__________________ The beginning is the most important part of the work -Plato
One common "mistake" that may cause people to think that all fire worms are not good, is caused by generalizing the predatory activity of Hermodice carunculata to all other fire worms ... well that is not reality! Hermodice carunculata is native from the Caribbean and is more or less dependant on specific food which means a specific coral or gorgonian. Besides this it does not have teeth so it has to lick them which implies that it has to spend hours in the same spot eating, so it is rapidly spotted and can be easily removed with a pair of tweezers or by hand wearing anti puncture gloves.
so Relax :-)
"I may of course, be egregiously wrong; but I cannot persuade myself that a theory which explains several classes of facts can be wholly wrong"...Charles Darwin. www.reefforum.net Zanclus canensces, cornutus, Kihikihi ou o zigzags always feed your Zanclus, Pomacanthus, Apolemichtys, Euxiphipops, all spongivores natural live sponge or try to, if you don't know how, see my article or ask me.