Blue sponge(?) on crocea shell: detrimental?

[RonSF]

I just noticed this fast growing thing growing on my 4" crocea's shell. Since I think I see sponge like operculum, I'm gussing that is what this is. The clam seems to have no problem with it so far (I had to agravate it a bit to get it to retract it's mantle a little to show this more clearly), but I don't want it to cause problems in the future. Is this very common?
Thanks,
Ron
BTW: The fogginess at the bottom is stuff on the glass. Sorry.

 

[acroporas]

Yes it is sponge. I was prepaired to say that most types of sponge shouldnt be a problem. But then I looked at the picture. I would remove it just to be save. It doesnt look very friendly to me.

 

[RonSF]

What determines friendliness in this type of relationship? I guess the growth rate is my biggest concern, but do some actually bore into the shell or do something directly harmful?
-Ron
BTW: Here's the photo without the link.

 

[acroporas]

Yes, some types of sponge produce acid to disolve rock/shell and bore into it. So yes some sponges can directly kill the clam.

 

[RonSF]

This thing came out of nowhere and grew really fast. I've had the clam for a year and a half, and not introduced anything in his vicinity in many months. I'm inclined to try to save a chunk of it for a live rock on the other side of the tank. Perhaps that is flirting with danger, though. Think a scrubbing with a toothbrush (out of the tank) will be enough to get rid of it from the clam's shell?
-Ron

 

[acroporas]

Yea, I would tooth brush and see if it grows back. I think sponges are cool so yes, I would probably try to get a pice growing on the live rock.

 

[Xmodius]

Nice sponge and clam.