Is my cleaner clam dead?

[lil.guppy]

I got 2 cleaner clams in today. Both sat on the top of the sand for a few hours and then one went into the sand. The other one is still sitting there. How can I tell if its dead or not?

 

[rs1831]

Is it open or is it closed? If its open and doesn't close when something goes next to it then its most likely dead.