Naked Science Forum

i think they do feel pain but don't remember it because they don't have a brain.  So they can react to pain (when they're being eaten they can 'call over the predators' of what is eating them, or they can send toxins to the bits that are being eaten and deter the eater.  So they're purely reactive/hormonal/emotional, not logical.

The reason they feel pain is because it's the motivation to make an effort to keep healthy - putting energy into surviving rather than dying.