That's the dreaded RED DEATH WORM!!!

If you so much as even make it think you see it, it can fire it's deadly, neurotoxin filled, razor barbed stingers out of the water at a distance of over TEN FEET! What's worse? The poison eats through your flesh like acid through calcium, turning your extremities black and dissolving your bones...

Nah, it's a bristleworm. Personally I wish I could find a huge fire worm, it would make a cool creature for a species tank, IMO.