Help figuring out what this is

[schmiddy]

I just setup a new 24 gallon nano and I bought some new live rock. I bought a rock that had another rock stuck to it. After about two days the rock look like it was splitting in half. I bumped in to the tank and it closed up. I think it's a clam or something. Does anyone know what it could be?

 

[cowfishrule]

is it that ball looking thing?
a thorny oyster maybe?

 

[schmiddy]

Yea its the little rock with the crack in it. Sorry I should have circled it. Is it ok to put coral around it?

 

[spunky]

i have the same thing and i have no idea what it is

 

[johnny&sin]

I bought 120lbs of FL live rock for my 110 gallon and my rocks are covered with those things... my boyfriend asked around and we were told they were clams of some sort...

 

[toxic_deviant]

One of my pieces of LR did the same thing. It opened up, so I brought it to to my Local Reef Specialty store. They said it was a mussel.