Fish With The Brains On Their Head. Zhuowei du and don b. The mystical artifact that creates them does so by altering their brains, making total destruction of the head the only way not involving sunlight or hamon to get rid of them, and even if you do use sunlight or hamon they can actually survive as long as they don't get hit in the head with it.
Among invertebrates such as cephalopod molluscs (octopuses), crustaceans, and insects, the optic lobes are right up front, as close as possible to the eyes. The cerebrum manages voluntary movements and the cerebellum manages involuntary movements (mainly balancing). Decapitation just creates a pissed off vampire head.