Here is a clip from Dr. Ron...
"Another type of worm that causes problems can be very large; I have seen individuals about 40 cm long and bright orange. These are thin compared to bristle worms, and although they do have small bristles along the sides, these are generally not apparent. These worms, Oenone fulgida, prey on snails and clams. They suffocate snails with a viscid mucus, and then eat the body, and apparently can bore into clams, such as Tridacna species and eat them as well (Delbeek and Sprung 1994). They live in holes in rocks and emerge to feed, but generally keep their posterior end in their home hole. They are nocturnal and feed in total darkness. When startled by a light they can retract back into their den with extreme rapidity. About the only way they can be removed from a system is by removing their piece of rock and manually pulling the worm out if it possible. "