Please Help Identify

[ReEf787]

Good afternoon everyone. I was doing some general maintenance on my 120 gallon reef tank and I noticed this little guy attached to my glass. As a point of reference, it's about the size of a small pea. Can anyone help identify it? I don't think it's harmful. Just wondering if anyone has ever had these kind of little critters attaching themselves to the inside of your tank glass. Thanks for all your help!

 

[twilliard]

Oh cool looks like a rock clam :-)

 

[tankstudy]

Looks almost like a mussel.

 

[ReEf787]

Yea... that's what I figured. But I wasn't 100% sure, so I figured I'd just put it out there for the R2R family to check out and chime in on :)