likely exhausted the food supply and then died out!Yeh those flatworms are ugly man. I had one on my glass, next day 4, next day 20, next day 100. Aghh, started freaking and saw some horror stories of tanks over run by them. For some reason mine started disappearing just as quickly after couple of weeks.
The cerata do apear to be too short to be this species, and the Nudibranch does still apear to have a 'head' but it has withdrawn. However, I am not an expert on Nudi so I may be inccorectHey Gunners, as far as your pics go looks like you've got "Part Of, no head and part of the torso" of Nudibranch Pteraeolidia Lanthia and not one of the colour variants either. Normally from QLD and come in heaps of pretty colous but i.d recommend to ditch it as it can cause painful stings