Never was there...

[Ricunger]

No clue what it is but it looks like a bi valve to me. when i pass a shadow it closes it's hard shell. I has never been there in the past 2 yrs that the rock has been facing that direction. About 2 months ago i noticed it. Any ideas?

 

[NanoReefWanabe]

looks like a rock boring clam...i used to have a bunch of them...cant find them anymore though...sorry i dont know the scientific name though...thatis just what i was told it was...