I find stuff like that all the time most of it is fossilized into my live rock once the saltwater erodes at it it starts popping out . so I'm always finding new things the neatest thing Ive found so far is a fossilized star fish , It's like a treasure hunt in your tank I find most of my discovery's after lights out , I uses a flash light with a red lens it don't seem disturb the fish or inverts at all , the red light picks up on things you don't see with the naked eye . I can never get bored roaming my tank at nite it's like a world of it's own .