Skin biting/chewing exists in some humans, part of the self-injury syndrome which is on the same neuropsychological spectrum as obsessive-compulsive disorder. It is classified as an "impulse control" disorder, and is often the result of abuse (either physical, emotional, or sexual) in childhood.
This form of self-injury (which can also include skin-cutting or skin-tearing behavior) is NOT a form of masochism, nor an attempt at suicide; rather, it creates a trancelike dissociative state which enables the person to escape environmental stressors or severe anxiety.
I am neither a psychologist nor a marine biologist, but IMHO there may be some relation between such behavior in cephs and in humans. (It has also been observed in non-human primates, and I believe certain other species.) I think stressors which do not allow an individual organism to lash out at the actual source, may turn the aggression inward to self-destructive behavior, which in turn releases endorphins that enable the organism to "cope" -- albeit in a very counterproductive way -- with the situation.
Do cephs produce endorphins? Steve-O, Jean, or Kat, perhaps one of you can answer that, as I don't know. I recently read that fish which have been caught on hooks were found to produce endorphins, presumably to counteract the pain of being pierced.
The neuropsychology of stress -- in both humans and animals -- is of great personal interest to me, so any further info on the subject of autophagy in cephs would be most appreciated.
Peace,
Tani