Please help me id whats going on with my clam mantle

[Tim L]

This looks like a bite mark or an infection. I caught my blenny biting my clam frequently. He had not extended. Until I removed the blenny he immediately extended.

 

[Tim L]

This looks like a bite mark or an infection. I caught my blenny biting my clam frequently. He had not extended. Until I removed the blenny he immediately extended.

 

[Tim L]

Photos from the top