Something is lurking in my rock

[Delareef123]

Hope I can get some direction on what I may have living in my rock. Here is a little background.
Purchased RSM 130 tank with rock and sand used about a month ago. The rock was very bare. So I had assumed the previous owner had the lights out on the tank for some time. Had no coralline or algae on the it. While cycling I notice little to no movement of anything on the rock.

I have sense added a clean up crew a few coral and 2 fish.

So....... last night I was checking out the tank and noticed a puff of sand was jettisoning from the rock. I figured it was just the hermits disrupting the sand on the rock. I then noticed the sand was coming out of a tiny hole in the rock. Witness the sand jettisoning out about 3-4 time. As if someone was burrowing in or burrowing out of the rock.

Looks like a little head/tail is poking out but can barley see it. At night when the lights were out I turned the flash light and "something" retracted into the hole real fast. Could not get a good look.

so any clues? bristle worm? what would be so hardy to outlive what coralline and other critters didn't live through?

 

[frisbee]

Eunice worm perhaps?

http://reefkeeping.com/issues/2003-04/rs/index.php

If it's not a worm, a Mantis shrimp is another possibility.

http://www.saltcorner.com/AquariumLibrary/browsegroupspecies.php?GroupID=157

 

[Delareef123]

thanks frisbee, doubt it's a Mantis as the hole is literally 1/4 to half and inch (13mm)
Also, what I think I saw when it retracted was a long body. The description of the Eunice seems accurate so far with the exception that they prefer sand. But without seeing the critter I have no idea.

do worms "spit" out sand or rock from there burrow?

 

[Oxylebius]

Any update or new photos you can post?