Can Anyone Tell Me What This Is--->??????

[es355lucille]

Thanks to everyone with the great ideas on what this thing could be. I really not much help here..... I will do what BCOrchidGuy is suggesting and stake it out one of these nights and see if I can catch him coming out. I have never seen it out any farther than you all see it there. If I scare him he goes deep into the rock and it takes it a full day to come back out to this position again.

Originally Posted by chandigz

That was my first thought some sort of bivalve (clam or mussel) Its a little tough to tell from the picture but it looks like you can see the hinge?