suggestions on ID

[JJ1234567]

I have a thing. It is living in a hole on my largest peice of Live Rock. It is green in color, and circular. the opening (mouth?) is about 5mm accross. I can never observe it for long, becuase once I come into sight it pulls itself back into the rock. I have read many books and posts, and have yet to run accross anything that looks like this. Any suggestions on what I might have?

 

[blout]

have you ever seen 2 little eyes staring out of it as it could be a mantis shrimp as they come in many diffrent colours aswell

 

[Christs_Knight]

if you gotta a mantis shrimp you would wanna get it out pritty soon.
Violent little buggers!

 

[steelhealr]

is it aiptasia? SH

 

[Chac]

Have a look at This Site, It has a list (& Pics) of some good & bad critters you will wind in a tank

 

[JJ1234567]

definitly not a mantis shrimp, although I have had my fair share of them. I have killed over 27 by my last count (I have a running total sheet). They all just kept coming out of a piece of rock, seems like i would get 6-7 at a time then a week with none. I havent had a problem with mantis shrimp in two months, so I think I finally got em all.

Thanks for the awsome website chac, but non of those pictures or descriptions seem to be what I have, I am really curious now.