Thats a crab on steroid but dude.. those worms..
I hate bristle worms as much as anyone who has been stung countless times by them, but the other day, I learned to appreciate them...I had an unfortunate death of a fish that I couldn't get from under the rocks. After about an hour, I saw a swarm of bristle worms devouring the dead carcass. By the next day, I saw a pile of worms and a skeleton.
These guys are serious detritus eaters. Sucks I had to learn to appreciate them from a fish death, but I don't see them the same way as I used to.