Is this a Bivalve?

I was diving today in Lake Worth Lagoon, Riviera Beach, FL.

I turned over a small rock and saw this small oval thing.

Help Leslie, is this a bivalve or something else?. It was about

the size of a penny, and in less than 5 feet of water.

It certainly is Anne. I'm terrible at bivalves & the very expensive book I bought on bivalves of southern Florida mostly shows clean dead shells.....not much of a help! Maybe this is some kind of oyster like a winged oyster or a jewelbox. There's a terrific site for shells from your area at http://jaxshells.org/ if you really want to try tracking this down.

Thanks Leslie, I'll see what I can find out.

Hi Anne,

I told Leslie that I had no idea what you'd found, but as I thought about it, I decided it MIGHT be a Pen Shell, laying on its side with the beak buried. There are several species, and I'm not sure I could narrow it to the species level without cleaning it up (assuming it does indeed belong to the Pinnidae). Leslie steered you right by sending you to the jaxshells site, I think. Check out this photo of Atrina rigida, and try to imagine what it would look like with a little stuff growing on it

http://www.jaxshells.org/417aa.htm

If we're seeing only part of the shell in your pic, Atrina seminuda is also a candidate:

http://www.jaxshells.org/514a.htm

Cheers,

Don

Thank you Don, I did go back the next day and took more photos, and I think it could be a pen shell. I am going to try to find it again and determine if it is alive or dead and get some more photos. Thanks, Anne