Hammer pest?

[.-=Jord=-.]

One of my hammer frags has not been fully opening. When I looked at its base I noticed what looks like a clam attached to it but I can't tell if it's just part of the hammer. It seems to open and closed when you watch it. Is this a pest, disease or just the hammer trying to split?

 

[Diesel]

Hitchhiker clam.
I don't think it will bring your hammer in danger, just keep an eye out on it.