too much of a lack of info for anyone to give you any meaningful advice.
watch it close, listen for clicking.

Bristle worms and mantis shrimp and pistol shrimp all look very different, but based on your description, it could be any of them.


best to be sure before you consider any advice or diagnosis.
wait until your lights are out, and put some food near where you saw it retreat (not with your fingers) and see if you can't get a better description.

the easiest way is to put the rock into your sump...or place the rock in fresh water and it will come out. some people have flushed them out with soda water...

Thanks I will try the freshwater idea. I just feed them with spirulina flakes and watched
his spot carefully he came flying out, he is about an inch long and so quick its amazing.
I really don't get it never heard the clicking before its creeepin me out a little.

my puffer would eat it

we freshwater dipped our liverock and flushed a pistol out. we didnt soak for very long and managed not to kill our coralline or worse all the bacteria in the rock. ive read a less shocking treatment is to soak in less saline water for slightly longer. its more gentle on the rock and will still make it uncomfortable enough for whatever critter is in it to vacate.

If it is that fast is sounds like a mantis shrimp to me they are lightning quick kind of freaky how fast they can move. Oh yah if it is Mantis whatch your fingers they are not called thumb splitters for nothing.

watch out that it doesnt climb out and get you at night, haha, just jokes.

Thanks lobster boy the tank is actually in my bedroom.
yuck anyone need a piece o rock nice coraline(free) you just have to grab it out.

:biggrin:

Unless your losing livestock leave the poor critter be. We pay big bucks to put living rock in our tanks and then do everything we can to kill all the life off.

I had a mantis shrimp in one of my tanks for 2 years and barely even noticed him, he never hurt anything. In fact for all I know he may still be around I never did figure out why he disappeared