is that pinched mantle?

[i have crabs]

Doesn't look like it too me but I couldn't say for sure since its a bit hard to tell from a picture, when my clam did it a couple times it looked like the edge of the mantle flesh would kinda scrunch up for the first while my clam would look normal except the edge looked weird and after a while it would start receding, freshwater dip worked both times I tried it