Need id?

[Ponraj A]

In my lepstrea coral there is an black covered layer like hole and in which we can see and white clam like thing is coming till the edge of the hole when lights are on and after that its going in. Its not fully showing up. Can anyone please id this whether its good or bad. Please refer the images below.

 

[Tahoe61]

Can not tell from the images, the first images looks like it's white and the second image looks like it's black? Not a barnacle? Vermetid? Could be a Gall Crab as they like to burrow in LPS, but the clam comment sounds like none of the things I listed.

 

[Ponraj A]

Thanks for your reply. I am not sure, its a doubt. Its like and this black screen and some times this white mouth like the shell is showing up and then going in after some time.