Nematoda
Nemotada is the phylum of roundworms. These roundworms are particularly important because they show cephalization, which occurs when nervous tissue becomes concentrated on one end of the organism. These organisms' head ganglia are the forerunners of human's brains. This is where we get the idea of a head, or anterior end. All nematodes have the same basic nervous system set-up: a head ganglia and four nerve cords running along the dorsal, ventral and lateral surfaces. This is why all three of the examples have similar nervous systems.