is that pinched mantle?

[daniella3d]

My large maxima is showing some receiding but it's only some part of its mantle and only one one side. Is that pinched mantle? The rest is fully extended and looks normal. You can see on the photo that the two parts on the right top right of that picture are not very well extended.

I did not think it was pinched mantle because it's not all of the clam showing this and I do have amphipods that are chewing on the clam at night despite me putting an actinic light ON all night. Dunno what to think??