Types of predator attacks and marks/scars on shells?

[dave r]

Pinholes are made by species of boring sponge. Slits or cuts are usually made by worms as mentioned above. Indented/eroded areas could be many things. As you say, Hoof Shell marks or Crepidula even, but they could also be attempts made by a boring predator like Muricidae or Naticidae. Large repaired breaks are usually the result of fish bites or crab attacks.
One other thing is a small hole on its own on a shell can be the result of octopus attack.