Killer Bristleworm?

[Hilary]

Okay, I'm the first person to scoff when folks say that their emerald crab, bristle worm or whatever "ate their fish". I'm wondering, though. I have a 12 gallon that's been up and running for over a year. I used to have small fish and sexies in it, but lost some of the fish when I lost power when away from the weekend. One sexy shrimp, the yellow watchman (about 2") and the priolepis goby survived. I added three trimma gobies, and all did well. Then the sexy disappeared. Drat. I added a little skunk cleaner. Gone the next day. I checked the water - all parameters good. Added a peppermint - gone the next day. Big water change. Found out my refractometer was off and slowly corrected the salinity (over about a week and a half). Thought it must have been the salinity since everything else seems to be okay. Added another sacrificial peppermint, and found half of his torso the next morning. It didn't look as if he had died and the one hermit had been after him - looked like he was cut in half. What the heck? I've never heard popping sounds from the tank so doubt there's a hidden mantis, but took the entire thing apart last night looking for the culprit. Found the little emerald crab, but put him back in after deciding that he can't be catching and devouring shrimp (plus I need him for the bubble algae). Also found that one of the trimmas is now gone. He was there in the morning. And now he wasn't. Took every coral and rock out and checked everything carefully, and the only thing I found was a very large bristleworm. I'd say it's 5-6" long, flat, very hairy. Thought it might be a fireworm at first, but coloring is just like the regular bristles we see in our tanks every day. Is there a possibility that it's been hunting in the tank?

[L8 2 RISE]

I'd say its possible if theres not enough food there for him. Nanos can be weird like this- critters will do stuff in them that wouldnt happen in your average tank... The only way to find out is to take the worm out and then see what happens with shrimp/ etc in the tank.

[Hilary]

Yea, he and his hairier buddies found a nice new home in my sump last night! Guess I'll keep checking parameters, and if headcount doesn't change within the next couple of weeks I'll sacrifice another peppermint.....

[igozoom]

I'd think that you would be missing some polyps as well if it's a fire worm. It certainly sounds like the work of a sneaky shrimp. Maybe if you could get a picture of the worm, someone could identify it.

[mogurnda]

It may also be a crab. Against my better judgement, I have kept very large (up to 4 ft) eunicid worms, and have seen them chomp things, but even the biggest would have trouble biting a pep in half. If they are the usual bristleworms (Eurythoe?), I'd think a six-incher would not be able to do it. That is pure speculation and opinion, so take it FWIW.

 

Mud crabs can tear things apart easily, and are remarkably cryptic. The I just pulled one from my 90 which must have survived 5 years and three tank moves.

[Hilary]

I agree that it looks like the work of some kind of crab - that shrimp looked like it had been snipped in half with scissors. I looked all over each rock under the MH and couldn't find anything, though that certainly doesn't mean there wasn't one flattened up against the rock in a hole. I've even started looking at the watchman suspiciously - it's actually grown about 1 1/2" lately. Well fed? On the other hand, the latest sacrificial peppermint is still living after 2 days and the two larger gobies have come out of hiding and are moving around the tank quite a bit more, so who knows? I