I've been looking for the title of this movie for years.?

I saw an animated Sc--Fi/Fantasy (Japanese?) movie on TV some years ago. It featured a boy who's name I think was Fry and he had a six legged cow like creature which got killed by worm things in a cave and there was an old guy with a metal plate on his head who lived near a lake with huge lilly pads and huge insects which try to suck out peoples brains, I think there were also 2 small floating aliens that were hiding on board a spaceship. Hope this wasn't just a weird dream I has... lol