Forgive my ignorance, but is the presence of a nervous system really the defining factor? What about mycelium in mushrooms, which operates as a signalling network?
I know a guy who will only eat windfall foods - plants that have died a natural death or fruit that have fallen from the tree (super hardcore fruitarian), and won't eat germplasm (I.e. Seeds - wheat, nuts, etc.) which seems to me, if the reason is ethical, to probably be the right place to draw the line.
Personally I'm an omnivore, but try to keep my meat consumption generally very low.
