Common clam question

[William Buchanan]

This isn’t a “typical” aquarium trade clam but one from the Atlantic Ocean. I was just curious if it was normal for really small fish to swim around in an open clam like this one

?

Here is a picture of a clam in my sump and one of the molly babies inside its mouth. I look down there and frequently see them swimming in and out.
Does this clam look okay?

 

[bluemon]

I don't think clams are supposed to open up all the way like that. I always feel like there is a membrane separating it at least on the sides. (market clams too)