ID Please

[dhouck]

Got this on a mushroom rock today. Didn't notice it until the shroom retracted. It's about 1 inch and it opens in the miidle of the pointed end.
When open, it raises slightly from the rock.

Thanks

 

[roka64]

Wow, that's a new one. So it only opens at the very front, where the lines come together?
Can you get a better pic?
Does it move slow?

 

[dhouck]

Yes, it opens where the lines come together. It moves like a clam: slowly opening then snapping shut when startled. I can't see a definitive hinge, though. The mushroom has since covered it, at least for today. Working on a better pic.

 

[dhouck]

These are the best I could do. In the closer one, you can see that it is open slightly. That's about the extent that I 've seen it open.

 

[roka64]

It looks like a clam that has attached its self to a horse shoe crab. I am really stumped at this point. Does the back end have a tail? Can you pick it up and take a pic of it;s underside?

 

[dhouck]

No, there isn't a tail and no horseshoe crab.

I found this pic online. It's called a heart cockle. It looks similar, but from other pics it seems cockles (though not specifically the heart cockle) are shaped like a regular bivalve clam. So that would mean that the creature in my tank is buried lip-down in the rock. And what I'm looking at is the hinge. Don't know if all cockles are shaped this way

 

[roka64]

You might have something there.